October 30, 2017 | Author: Anonymous | Category: N/A
- inclusive; from solar irradiance input to electric delivery on the. Accounting Solar Thermal Pam ......
☼ SPOTLIGHT
ON
SOLAR THERMAL MODELING ☼ THERMOFLOW
Thermoflow Software
Solar Fields & Solar Fields with Storage
Parabolic Troughs
Linear Fresnel Collectors Engineering And Construction Estimator) was introduced as a Thermoflow provides software for companion to GT PRO in 1998. design, simulation, and cost Today, PEACE is integrated into estimation of power, cogeneration, r mof l ow’ se nt i r es ui t e .PEACE process, and heating plants. Starting The Solar Towers provides physical equipment specs, in 1987 with its flagship program GT PRO™,The r mof l ow’ ss of t wa r es ui t e capital cost, labor estimates, and estimated installed costs for User-defined Fields has grown to include seven e ngi ne e r e d”c ompone nt s ,i nc l udi ng powerful, yet easy-to-use programs “ many elements used in solar to analyze the spectrum of power Condensers & Cooling Towers thermal power plants models. generating technologies in use today, and under consideration to THERMOFLEX & PEACE: me e tt omor r ow’ sde mandi ng Solar Thermal Modeling challenges. These powerful tools are used for As of 2012, Thermoflow has sold heat balance design of thermal Direct Contact Water Cooled Air Cooled over 7500 program licenses to power systems, and for simulation companies in more than 75 of off-design plant performance. countries. This proven track record THERMOFLEX is flexible. It make sThe r mof l ow’ ss of t wa r es ui t e provides the user full freedom to the most widely-used, and wellconstruct flowsheets using respected in the power generation component models available in its Mechanical Wet/Dry Natural industry. toolbox. THERMOFLEX has all Draft CT Mechanical Draft Draft CT the components needed to model This pamphlet focuses on solar complete power plants of virtually thermal power and heating cycles, a every type, or to model only a small Feedwater Heater Trains—shell & tube LP & s mal ls ubs e toft hef ul ls ui t e ’ s subsystem such as a pump and HP heaters, deaerators, flashtanks, generalcapabilities. You can learn more pipe. purpose & general fluid heat exchangers about the whole suite at thermoflow.com, or by contacting THERMOFLEX Toolkit— Thermoflow directly. Component Models Thermoflow Software
THERMOFLEX™,t oge t he rwi t h PEACE™,pr ov i de sde s i gn, simulation and cost estimation for solar thermal power and heating cycles. First released in 1995, THERMOFLEX has been under continuous development ever since. Today, THERMOFLEX is the most well-proven fully-flexible heat balance program available. PEACE (an acronym for Plant
2 THERMOFLOW
The icon toolkit includes all the component models and fluid properties needed to build solar thermal power plant models. The model boundary can be allinclusive; from solar irradiance input to electric delivery on the high-voltage side of step-up transformers. Alternatively, the model can include only a steam
FWH w/ flashback
Flashtank
Deaerator (open heater) A B
General Fluid HX
FWH w/ pump forward
turbine and its feedwater heating train, or anything in between.
These two pages show only a small subset of the full selection of THERMOFLEX / PEACE model icons - those typically used in solar thermal power plants. As of 2012, THERMOFLEX / PEACE collectively include over one hundred and seventy-five (> 175) different icons. THERMOFLEX includes built-in properties for seven (7) fluid types representing hundreds of specific fluids used in power and process applications.
Solar Thermal Toolbox Steam Turbines
Solar Boilers
Condensing, Non-Reheat (single & multi-casing)
Back Pressure
Shell & Tube Superheater
Condensing Reheat (single & multi-casing) Shell & Tube Evaporator Fluids—seven types with built-in properties to represent hundreds of specific fluids
Water: subcooled, saturated, superheated, & supercritical
Heat Transfer Fluids: DOW, Solutia, Paratherm, Duratherm Molten Salt, user-defined, etc.
Dry & humid air, combustion products, pure gases such as N2, CO2, etc.
Fuels: solid, liquid, gaseous
Brine: seawater & brackish water
Refrigerants: subcooled to supercritical
Shell & Tube Economizer
Ammonia/Water mixtures
Gas Turbines & Boilers—Supplemental steam,
Pumps, Pipes, Headers, Valves, Processes—
backup heat input, parallel heating systems
Network fluid flow modeling
LP IP
HP
GT PRO Gas Turbine Library (>370 engine specs) Heat Recovery Steam Generators (HRSG)
RH1
RH2
Pumps—multi-stage BFP, vertical turbine CW pumps, vertical condensate forwarding, single stage multi-purpose Piping systems—physical models with straight runs, headers, fittings, valves, branches, elevation changes, etc.
User-defined Boilers `
SA
Recirc
Package Boilers
PA
Temp
Fired Utility Boilers— coal, oil, gas
THERMOFLOW 3
Solar Field Component
Solar Field Model Options
In solar thermal plants, the solar field supplies some or all of the heat needed by the cycle. The field may deliver hot thermal oil, hot water, saturated steam, or superheated steam. THERMOFLEX has a completely user-defined solar field where the user directly specifies solar field heat input to the working fluid used in the cycle. In this case, no detailed field modeling is done by THERMOFLEX, r a t he rt heus e r ’ s specified field performance is applied directly. This simple approach makes including manufacturer-specified performance quick and easy. THERMOFLEX also allows the user t omode lt hes ol a rf i e l d’ st he r mal hydraulic-optical performance directly, in detail. THERMOFLEX
computes number and length of each collector row, the total solar field size, fluid pressure drop, land use requirements and estimated field cost based, on desired field performance. At off-design the solar field model estimates field heating capacity and fluid-side pressure drop for given solar irradiance and field operating conditions. The THERMOFLEX solar field model is a general line collector model with options to pick specific parabolic trough and linear Fresnel collector configurations, and ability to specify user-defined collector characteristics. Design Point
The Main Inputs menu for design calculations is shown here. The Collector Hardware & Characteristics menu is shown at the top of the next page. These two
menus allow the user to specify the desired field thermal-hydraulic performance and the physical and optical characteristics of the collector used. Default values are supplied for all inputs, and the user can always adjust the inputs to suit their needs. At design, THERMOFLEX uses t he s ei nput st oc omput et hef i e l d’ s thermal-hydraulic performance and estimate the collector size and land requirements. The solar field consists of a number of flowpaths connecting cold supply header to the hot return header. Each flowpath spans one or more collector rows. Large trough fields typically use two collector rows per flowpath so the hot and cold headers are at the same end of the row banks. Some linear Fresnel collectors, especially with direct steam generation use one flowpath per collector row so cold fluid enters at one end, and steam exits to a steam drum at the opposite end. Smaller roof-top heating collectors often have many collector rows per flowpath to accommodate the desired temperature rise in a limited footprint.
Main design-point model inputs. These are desired flowrate, exit temperature, pressure drop, tube velocity (mass flux), and optical efficiency for normal ray strikes. All inputs have default settings that are easily reset as needed. The field model or the heat consumer can ultimately de t e r mi nef l ui df l owr at epar t l ybas e dont he‘ f l owpr i or i t y ’ s e t t i ng.
4 THERMOFLOW
Design Point Model Inputs
Collector library includes layout and optical properties for various technologies. This built-in data is easily adjusted to model a particular collector.
Incident Angle Modifiers (IAM) factors adjust nominal optical efficiency to account for nonincident ray strikes. IAM data may be edited to reflect the specific characteristics of any line collector. The data is typically generated by collector manufacturer using ray-tracing programs. This is key to determining how much irradiance is incident on the receiver, which ultimately affects field efficiency and required size to achieve desired heating.
This menu is used to specify collector cross-section, receiver dimensions and heat transfer characteristics, and desired field arrangement. This data can be selected from a library of built-in collectors, and/or be edited directly.
The Flow Path Hardware menu (below) is used to specify hydraulic parameters affecting the pressure drop from cold header to hot header. The fittings specified here together with the straight run of receiver tube with its specified roughness are used
Receiver tube roughness, and number/type of fittings installed in each flowpath can be set automatically, or by user input. These parameters impact the computed field pressure drop, and hence pump size and power requirements.
to compute an equivalent length of straight piping. The pressure drop is computed using that length together with flow conditions and temperature/pressure-dependent fluid properties.
Collector cross section data, as set by user, or automatically by THERMOFLEX, is displayed as one of the graphic output reports.
THERMOFLOW 5
Solar Resource
plant designer has limited access to Site irradiance levels and the relative detailed site-specific irradiance data, yet still wants to compute a solar sun-collector position are two key mode l .I t ’ sagr e atwayt o“ ge t parameters for the solar plant t a r t e d”ort oc ompa r er e l at i v es i t e designer. Once a system is designed s performance. (sized), its heating ability at different times of day, on different days of the THERMOFLEX estimates the DNI year is heavily dependent on the and relative sun-collector angles site's solar characteristics. using a model of relative sun-earth THERMOFLEX provides four ways positioning as a function of time of to input irradiance and relative sun- day and day of year. Ground-based collector positioning. Each method irradiance is computed using an estimate of atmospheric is designed to make it easy to use assumptions, actual measurements, transmissivity. This atmospheric representation is most applicable for or data from statistical analysis, sites with a large number of sunny such as TMY3 data. days per year, those typically most desirable for solar thermal plant 1. Estimated from Site Data siting. This method is most useful for upSolar Resource
front scoping studies where the
This method makes it easy to pick a
time of day, and a day of year for a specified site, and rely on the program to compute irradiance and solar angles. The input menu for this method is shown below. The Estimated Irradiance panel along the top includes the solar-specific inputs needed to estimate irradiance. Site altitude is set elsewhere. The daily variation in DNI and ANI (Aperture Normal Irradiance) are shown as a function of solar time as the green and blue lines, respectively. The graph title shows a summary of the conditions used to estimate the irradiance together with the length of the solar day. Daily peak ANI and daily average ANI values are shown to the right.
Plot shows estimated variation in DNI and ANI throughout the day. Site-specific data and day of year used in the estimate shown above the plot. Daily peak ANI and daily average ANI values are shown to the right.
6 THERMOFLOW
Irradiance and Solar Angles
2. User-defined DNI & Local Time
More detailed plant design and simulation often uses irradiance data measured from ground or satellite. This data is available from a number of sources. In the US, data for hundreds of sites is available in TMY3 datasets available from National Renewable Energy Laboratory (NREL). TMY3 data statistically represent conditions at a specific site by analyzing measurements made over decades. Data sources are available for other locations worldwide, some for free and others on a commercial basis. Regardless of the source, the solar data is characterized by site longitude, latitude, altitude, local time, day of year, and irradiance (DNI, diffuse, total). THERMOFLEX includes this method of solar data input to facilitate use of TMY3 (and similar) data sets. The Site location and current time panel shown on the input menu below lists the input parameters needed. THERMOFLEX computes the solar time from this data using an equation of time. The relative sun-collector positioning is used to compute azimuth and zenith angles associated with the specified day and time.
3. User-defined DNI & Solar Angles
This method is used to directly specify DNI and location of the sun in the sky. THERMOFLEX computes Aperture Normal Irradiance (ANI) from this data using inputs for collector orientation on the earth (N-S, E-W, or other) and tilt from horizontal. This method is used to specify “ t y pi c al ”i r r adi anc ec ondi t i onf or collector design, or when scanning through a range of conditions for off-design simulation.
This approach requires the least amount of input to THERMOFLEX but usually requires the largest amount of independent calculation outside THERMOFLEX to determine this input value. Solar Angles
The diagram below shows the definition of solar angles relative to collector midpoint. The collector is not shown, but may be located with primary axis along N-S, E-W, or anywhere in between. Large collectors are typically installed with zero tilt, but the model allows specification of tilt away from the horizontal if needed.
z (Zenith)
4. User-defined ANI
This method is used to directly specify Aperture Normal Irradiance (ANI), that is how much beam irradiance falls normal to the collector aperture. As such, it has a single input value. In this case, THERMOFLEX simply applies this value and ignores collector orientation, solar angles, and other inputs that would be used to ultimately compute this quantity.
Sun
S
n (North)
Zenith Angle
Altitude Angle
Azimuth Angle
e (East)
THERMOFLOW 7
Kramer Junction SEGS VI
Model Overview
The overall heat balance result from a THERMOFLEX model of the Kramer Junction SEGS VI plant is shown below. The well-known facility is a single reheat indirectly heated Rankine cycle with six feedwater heaters. The solar field heats Therminol VP-1 which flows through the solar boiler to make and reheat steam. The steam turbine exhausts to a water cooled condenser serviced by a wet cooling tower. The model is a complete representation of the entire facility including solar field, solar boiler elements, steam turbine, feedwater heater train, condenser, cooling tower, and associated balance of plant. For a given model run, the minimum required inputs are (1) Ambient conditions, and (2) Solar irradiance data. The program computes gross
power, net power, auxiliary electric loads, as well as flow, pressure, temperature, and enthalpy throughout the cycle. The result below is for the 100% solar loading case at design ambient conditions. The plant model produces 35 MW gross electric power, consumes 2.6 MW of auxiliary power, and produces 32.4 MW net power. In the diagram only key state data are displayed for clarity. However, the user can display the state data at every node, and each icon includes a series of text and graphic output reports for each run. Model predictions match design point data to a high level of fidelity. Summary Report
Summary results for each component are available by doubleclicking an icon from the overall heat balance view. The display
above is the summary display for the solar field. THERMOFLEX includes a library of heat transfer fluids that are commonly used in solar applications. The fluid library includes thermal and physical fluid properties used in pressure drop and heat transfer calculations. In this model Therminol VP-1 circulates within the field and the solar boiler. The solar field diagram shows the state of the Therminol (pink fluid) entering the field on the left, and the field delivery condition on the right. A performance summary is shown in blue in the lower left corner. In this model, DNI is 916 W/m2, total heat
Overall design point heat balance result from a THERMOFLEX model of the Kramer Junction SEGS VI plant. 8 THERMOFLOW
Select Model Results & Output Reports
transferred to fluid in the field is 92.7 MW, and the fluid pressure drop from receiver inlet to exit is 6.5 bar, or about 27% of exit pressure. Detailed Reports
A series of detailed text and graphic reports are presented to describe the computed heat balance, the physical equipment description, and for Steam Turbine PEACE components, estimated THERMOFLEX output reports equipment and installation costs. include text and graphics to describe steam turbine performance, The field size and layout report is configuration, and cost. Reports di s pl a y e dbe l ow.Thebi r d’ s -eye include detailed heat balance results view shows the collector rows are oriented North-South. Fifty (50) U- in and around the turbine, section efficiencies, turbine casing shaped flowpaths are arranged in one hundred (100) collector rows in configuration, leakage schematics, estimated turbine generator size, two row banks. Fluid enters from weight, capital cost, and installation and returns to headers in between labor. row banks. Major dimensions are listed along with total field aperture and required land area.
The steam turbine expansion path, Mollier diagram, is shown in the top right corner above. Extraction pressures for feedwater heaters are shown along the
path which consist of an HP section and an IP/LP section with steam reheat in between. Steam exhausts at 80 mbar with a quality of about 90%. PEACE cost and installation estimates are based on equipment size, weight, and configuration details. A series of reports present this data. The estimated elevation view for the steam turbine is shown below along with a summary of overall dimensions for the turbine and its generator. The steam turbine design model is entirely dynamic, so any changes to design parameters are reflected in these reports, and in the cost and installation labor estimates.
Sol arf i e l dbi r d’ s -eye view output graphic showing field arrangement and computed land area, aperture area, flowpaths, etc.
THERMOFLOW 9
Solar Power with Thermal Storage
One way to mitigate some problems associated with varying solar On“ g ood”day s ,i n“ s unny ” availability is to include a thermal locations, pure solar plants (see preceding pages) produce electricity storage system to store heat captured by the solar field. The for seven to thirteen hours of the storage system decouples the solar day. As the sun rises, sets, and is f i e l d’ sabi l i t yt oc apt ur ehe a tf r om blocked by clouds, the energy t h e p o w e r p l a n t ’ s d e ma n d f o r h e att o capture rate changes; sometimes achieve a desired power production very rapidly. The steam power level. This capacitance effect is pl ant ’ se l e c t r i c i t yout putf ol l ows solar capture rate up to a point, but useful to ride out transients, and for time-shifting the power production cannot always follow without tripping off-line. In these situations, relative to the sun. Storage systems t hes ol arf i e l dmus t“ dump”e ne r gy , potentially help plants dispatch power in a more predictable and or defocus to prevent overheating reliable fashion. So, rather than the fluid and field components. producing a continuously variable During startup, or following a trip, power level throughout the day, a the solar field and power plant are plant can deliver a fixed baseload restarted, and resynched to the grid. level for a more predictable period. This process takes time, and is not Or, a plant could be dispatched to always possible given the time of meet morning and evening peak day, or prevailing and expected demands experienced by many weather conditions. utilities. The Storage Issue
10 THERMOFLOW
Storage Systems
Various types of thermal storage systems have been tried in pilot projects and in commercial power plants. A number of advanced and novel concepts are currently the focus of research efforts. The basic forms of storage are (1) direct oil storage, (2) indirect storage using a second liquid such as salt, (3) indirect using a solid such as concrete, and (4) indirect using a phase change material to capitalize on relatively high apparent heat capacity from melting and freezing suitable materials. Early storage projects used direct oil storage. Such a system was implemented for a period of time at Kramer Junction, but is no longer operational. In this system, some thermal oil from the field is diverted to insulated storage tanks instead of
Andasol 1 Power Plant
From network THERMINOL VP-1
Solar Field DP = 5.378bar Aperture defocused = 0 % Heat from field = 100 % 156 of 156 flowpaths in use
34.15 p 291.8 T 970.6 h 1079.4 m
used to make steam. When the heat is needed later on, hot oil is pumped from the storage tanks to the solar boiler where it is used to make steam. This system increases the amount of thermal oil onsite, which is problematic for permitting reasons, and economic reasons because thermal oils are relatively expensive.
36.88 p 296 T 980.1 h 544.4 m
DTc = 4.019 C
5.582 291.9 842.4 892.2
p T h m
DP=2.722bar
36.88 p 292.5 T 972.1 h 1079.4 m
DP=2.735bar
36.88 p 288.9 T 963.9 h 535 m
26.05 p 391 T 1212 h 1079.4 m
26.05 p 391 T 1212 h 535 m To network
28.77 p 392.2 T 1215 h 1079.4 m
DP = 3.201 bar
Heat Exchanger
UA = 25785 kW/C DTLM = 4.952 C
1696.3 kW
40.09 p 392 T 1214.7 h 544.4 m
DTh = 6.019 C
DP = 3.24 bar
2.341 p 386 T 984.1 h 892.2 m
274.1 kW
Level = 38 %
Level = 62 % 1.854 291.8 842.1 892.2
Cold Tank
p T h m
2.341 p 386 T 984.1 h 892.2 m
Vol = 14524 m^3
Storage system: charging mode
Currently, commercial-scale solar thermal storage is being designed and built using indirect storage. The storage medium is molten salt, not thermal oil. Molten salts are advantageous because they have high volumetric heat capacity, can be stored in atmospheric tanks be c aus eofs al t ’ sl owv aporpr e s s ur e , and are relatively inexpensive. Two-tank Molten Salt
The Andasol plants located in Granada Spain, and other similar facilities, use a two-tank molten salt storage system. The system is c ompr i s e dofs e pa r a t e“ hot ”a nd “ c ol d”i ns ul at e ds t or aget anksof roughly equal volume. The schematic above shows such a system operating in charging mode.
Hot Tank Vol = 14524 m^3
Stored fluid: Nitrate Salt 60% NaNO3 - 40% KNO3 by wt
Molten salt is pumped from tank to tank through the salt-to-oil storage HX as the storage system charges and discharges. When the solar field captures more heat than is needed by the power plant, some thermal oil flows through the storage HX to heat the salt flowing from the cold tank to the hot tank. This charges the storage system with the excess field heat. In contrast, when the solar field absorbs less heat than is needed to run the power plant, cool thermal oil flows in the other direction through the heat exchanger where it is heated by salt flowing from the hot tank to the cold tank. Thermal oil heated by the storage system is combined with any oil heated by the field and used to make steam for the power plant. Discharging the storage allows the
bar - p C-T kJ/kg - h kg/s - m
power plant to make power when needed or desired, as opposed to being held entirely captive by the s un’ sav ai l abi l i t y . Solar fields with two tank storage systems have been designed to provide between six and twelve hours of full load power without sunshine. Andasol 1 Plant Model
THERMOFLEX was used to create the model shown to the left. It is a 50 MW reheat Rankine cycle similar to the Andasol 1 solar thermal power plant located in Granada, Spain. It has five feedwater heaters and steam is condensed in a water cooled condenser serviced by a wet cooling tower. A solar boiler with parallel reheater produces and reheats steam in shell-tube heat exchangers. The
THERMOFLOW 11
Daily Plant Operation
heaters use hot thermal oil (Therminol VP-1) provided by the solar field. A two-tank molten salt storage system is used to store excess heat generated by the oversized solar field, when possible.
field and storage system are modeled together in a single icon (#16) which has built-in logic to charge and discharge the storage system as the field heating ability changes throughout the day.
Steam conditions are lower than with fossil fired plants because they are limited by thermal oil operating temperatures. Nominal steam turbine conditions are 100 bar, 381 C at HP admission, and 18 bar, 381 C at reheat admission. At nominal conditions, approximately 535 kg/s of hot thermal oil is required to run the power plant.
This system is 100% solar; there is no backup thermal oil heater to provide heat when the solar field is out of service, or unavailable due to a lack of sunshine.
The solar field is sized at noon on the Vernal equinox with a solar multiple of 1.5. The storage system capacity is 1045 MWhr, and the storage heat exchanger is rated at just under 140 MW. Operating on storage alone, this plant can operate for about 7.5 hours at rated discharge capacity. The model was developed using ambient conditions typical of the Andasol 1 location in southern Spain (37.1 north latitude, 1100 masl). The solar field is oversized for summer operation and can heat almost twice as much fluid at noon than is needed to run the power plant at its rated load. The solar
12 THERMOFLOW
Operation
Storage system operation is naturally a time-dependent process. THERMOFLEX calculates steadystate models, so modeling plant operation with storage is done with a quasi-steady approach using a series of runs, each representing a single slice of time where the plant is assumed to operate in steady-state. E-LINK is the tool used to carry out these runs where the inputs are entered in Excel, and 1000 the outputs are 900 presented in Excel.
The model shown in preceding page was run from midnight to midnight on day 173, the summer solstice. The initial condition for hot tank storage level is the value computed byt hepr e v i ousday ’ ss i mul a t i on. THERMOFLEX’ sbui l t -in solar irradiance model was used to estimate DNI and solar angles throughout the day. The latitude is 37.1 degrees north, the location of Andasol 1 in Granada, Spain. The following series of charts show variation in selected parameters throughout the day. In each case, the x-axis is solar hour of day.
DNI
800
In Excel, the storage s y s t e m’ ss t a t eatt he end of the current time step is fed forward as the initial condition for the next time step. Quasisteady modeling is a useful tool for approximating plant operation over long time periods where the transients encountered are fast
DNI, W/sq.m.
The solar field consists of a large number of parabolic trough collectors that focus solar energy on a receiver tube carrying the thermal oil. The oil is heated as it passes through the field.
Simulation of Daily Plant
relative to the time step.
700 600 500 400 300 200 100 0 0
3
6
9
12
15
18
21
24
These calculations use irradiance from the built-in sun model. This plot shows computed variation in Direct Normal Irradiance for Day 173 at elevation of 1100m at 37.1° North. This is the key driver governing heat input to the plant.
Thermal Storage
100 Hot tank level
80 70 60 60
50 40
390
50
20 10 0 0
3
6
9
12
15
18
21
24
Hot and cold tank levels change throughout the day. In this model, the hot tank is about 30% full at midnight, the starting time for this quasi-steady analysis. The hot level drops steadily as the demand for hot oil remains constant. Once the hot tank is empty, the storage system shuts down, and no oil is delivered to the network, so the power plant shuts down. At about 6:30AM, the field is capable of heating more oil than required by the network. At this time, the storage system goes into charging mode and the hot tank level begins to rise. The rate of rise increases initially as the DNI level rises. Just before 9AM the storage system charge rate hits its limit, and the hot tank level begins to rise at a constant rate. At about 2:45PM the hot tank is full and the storage system cannot absorb anymore heat. At about 5:30PM the storage system begins to discharge because the solar field cannot produce enough hot oil to satisfy demand by itself.
385 40 30
380
20 375
Main steam flow
10
Temperature, C
30
Main steam flow, kg/s
Hot storage tank level, %
90
Main steam temperature 0
370 0
3
6
9
12
15
18
21
24
Plant loading in this model is established by setting a desired hot oil flow on the solar field with storage icon, #16 in diagram on previous page. The delivered oil temperature depends on the heating source. When the field heats all the oil, it is available at its design temperature. The oil temperature drops whenever some of the heat comes from storage. The result is variable steam flow to steam turbine, and variable HP and RHT steam temperatures. This plot shows main steam flow of just below 50 kg/s at 373 C when the storage system is the only heat source. During the day, the steam flow rises by about 4% and is available at 382 C due to higher oil temperature from the field.
This plot shows Therminol flows from the solar field, from the storage system, and to the storage system as a percent of flow delivered to the solar boiler. The solid line shows field flow. The long dashed line shows storage discharge used to makeup field shortfall. The short dashes represent flow used to charge the storage system.
The discharge flow mixes with any field-heated fluid and is delivered at the mixture temperature. During the evening and overnight period the storage system provides all Therminol. During the daytime, the field alone is capable of satisfying flow demand and the storage system is operated in charge mode or is s hut downi fi t ’ sf ul l .
Flow as percent of delivery flow, %
The early summer sunrise allows the field to begin to produce hot oil just after 5AM. Field oil heating continues until almost 7PM. The flowrate increases until just before 9AM when the storage system charge rate hits its maximum due to maximum salt flowrate. This capacity limit is in place until just before 3PM 250 when the storage tank becomes filled to Therminol from field capacity. At this time, the storage system shuts Therminol from storage down and mirrors are defocused to restrict field 200 heating to that needed to just meet demand Therminol to storage flow. Starting around 5:30PM, the field flow 150 begins to drop because of waning sunlight. 100
50
0 0
3
6
9
12
15
18
21
24
The field flowrate is large enough to begin to charge the storage system at about 6AM. The charging period that lasts until just before 3PM. The cap in charging flowrate occurs when the storage system charge rate hits its maximum, as implied by maximum salt flowrate from tank to tank. The charging flow quickly drops to zero at about 2:45PM when the hot tank is full.
THERMOFLOW 13
Integrated Solar Combined Cycle (ISCC)
contribution is used to augment plant capacity, or to replace gasCycle (ISCC) fired duct burners to generate extra Integrated Solar Combined Cycle steam during peak power demand plants are a gas turbine combined periods. In many warm locations, cycle with a solar thermal plant to power demand peaks in the mid-day add heat to the combined cycle. hours of the summer when While solar-captured heat may be significant air conditioning loads incorporated in many ways; it is typically introduced as high pressure occur. This demand profile is wellt c he dt oas ol arf i e l d’ sc a pa c i t y saturated steam, mixed with HRSG ma profile. HP steam, and superheated for admission to the steam turbine. THERMOFLEX together with GT THERMOFLEX can readily model PRO deliver rapid plant scoping this, or any other arrangement capability together with flexible under consideration. plant modeling features. Here, GT PRO was used to create the initial Medium to large scale (100 to 500 MW) ISCC plant designs have been plant model, where solar heat input wasmode l e dasan“ e xt e r nalhe at proposed where the solar addi t i on” .Af t e r war ds ,t heGTPRO Integrated Solar Combined
design was imported to THERMOFLEX and the solar field and solar boiler were added to generate steam in the model shown below. The plant design is derived from a heat balance provided courtesy of Siemens Industrial Turbomachinery. It is a 2x1 ISCC with two Siemens SGT-800 gas turbines exhausting into fired single pressure HRSGs making steam at 83 bar / 565 C for admission to a condensing steam turbine. Steam is condensed in a dry air-cooled condenser. The parabolic trough solar field nominally adds 50 MWth to augment HP steam generated in the HRSG.
THERMOFLEX model of a heat balance provided courtesy of Siemens Industrial Turbomachinery. It is a 2x1 ISCC with two Siemens SGT-800 gas turbines exhausting into fired single pressure HRSGs making steam for admission to a condensing non-reheat steam turbine. Model includes a parabolic trough solar field that adds just over 49 MWth to the plant as saturated HP steam. The solar-generated steam is about 80% of duct burner heat input at this condition, and represents about 32% of the steam flow to the steam turbine.
14 THERMOFLOW
Under desert-like ambient conditions, 35 C, 35% RH, 928 mbar, and with 49.3 MWth heat input from the solar field, the plant generates 157.6 MW gross electric output using 276.3 MWth LHV fuel input. Considering the fuel-free solar contribution, the plant operates with a 57.1% gross LHV electric efficiency, considerably higher than typically achieved with one pressure non-reheat GTCC plants.
Solar Thermal Desalination
Solar Thermal Desalination
Heat input is provided by the combination of a solar field and natural gas-fired boiler, installed in parallel. This solar-fossil hybrid de s i gnl e v e r age st hes i t e ’ ss unny climate and its proximity to natural gas fields. The hybrid design can produce power and water 24 hours per day without a solar storage system. The desalination system condenses steam turbine exhaust Electrically-driven RO is typically and produces potable water from used in small to medium-scale water seawater. It takes the place of what production facilities. Thermallywould be a steam condenser in a driven MED and MSF use low to pure power plant. moderate grade heat, and are used in most of the medium to large-scale The solar field uses Linear Fresnel Collectors (LFC) with direct steam systems installed today. generation (DSG). It consists of THERMOFLEX together with three sections; one to preheat water, PEACE can model these desalination one to evaporate water, and the final processes at the design-point and at section to superheat steam. The off-design conditions. Model results evaporator is designed to produce include detailed thermodynamic 30% quality steam. A steam drum states, performance metrics, and separates the phases; liquid recircuinstalled system cost estimate. lates to evaporator inlet, and dry steam flows to the superheater field. The THERMOFLEX model at right was supplied courtesy of Solar Power Group, GmbH. It models water & power producing plant in the coastal Surt region of Libya, owned by the Libyan Ministry of Energy. Nominally, this plant produces 15,000 m3 per day (3 MIGD) of potable water and has 15 MWnet electric capacity. Desalination of sea and brackish water to produce fresh water for domestic and industrial uses is becoming increasingly important in many places around the world. Presently, the major desalination processes in use are Reverse Osmosis (RO), Multi-Effect Distillation (MED), and Multi-Stage Flash (MSF).
A single-casing steam turbine operates at high speed with a reduction gear coupled to a synchronous generator. Nominal turbine inlet steam conditions are 55 bar, 400 C. Three steam extractions provide steam to a deaerator and two higher-pressure feedwater heaters. Water is preheated to about 190 C before the economizer section of the solar field. Feedwater to the gas-fired boiler comes directly from the feedpump. The desalination system is comprised of two parallel units, each having a nominal capacity of 7,500 m3 per day (1.5 MIGD). The MED design has a nominal performance ratio of 10.4 (gain output ratio of 9.4). This high level of efficiency is achieved by using twelve effects over a temperature range of 30 C.
THERMOFLOW 15
Solar Tower Fields
Solar Tower Field
Tower field optical performance is computed outside THERMOFLEX using any of the available tools, such as Solar Advisory Model (SAM), HFLCAL, etc. and specified as input to the tower icon. The optical performance efficiencies are specified as a two-dimensional matrix of data parameterized by solar zenith and azimuth angles.
The Solar Tower and Solar Tower with Direct Storage models were introduced in Thermoflow 22, February 2012. These models provide design and simulation for both external and cavity receivers with surround and directional (wedge-shaped) fields. The receiver can be used with water/steam, molten salt, thermal oils, and air and The tower model computes the other gases. Storage is available thermal-hydraulic performance of when using molten salt or thermal the tower supply pipes, receiver, and oils only. return pipes. For models with storage, the system pump with The tower field can be integrated into power and heat cycles using the optional energy recovery turbine and tank system is automatically full feature set available in handled by the model. The storage THERMOFLEX. system is sized in design, and used
at off-design in either charging, discharging, or off-line modes. The model provides for ability to limit heat input, and logic for shutdown under low DNI conditions. Design Point
The Main Inputs menu for design calculations is shown here. The Collector Hardware & Characteristics menu is shown at the top of the next page. These two menus allow the user to specify the desired field thermal-hydraulic performance and the physical and optical characteristics of the collector used. Default values are supplied for all inputs, and the user can always adjust the inputs to suit their needs. At design, THERMOFLEX uses these inputs to compute t hef i e l d’ st he r mal hydraulic performance and estimate the collector size and land requirements.
With external receivers, the reflector field consists of a large number of heliostats surrounding the tower, perhaps biased to one s i det omat c ht het owe r ’ s output to the utility needs. With cavity receivers, the reflector field is biased towards Main design-point thermal-hydraulic model inputs include desired flowrate, exit temperature, pressure drops, and heat losses from pipes. The solar multiple and desired number of fields are the northern side of the used for sizing. All model inputs have default settings that are easily reset as needed. The field tower (above the model icon itself, or the heat consumer (a solar boiler in many cases) can ultimately determine equator) so they can f l ui df l owr at epar t l ybas e dont he‘ f l owpr i or i t y ’ s e t t i ng.
16 THERMOFLOW
Model Features
Collector library includes layout and optical properties for various technologies. This built-in data is easily adjusted to model particular plants.
S o la r T o we r E ff ic ie nc y 8 5 0 M Wt S urro und F ie ld - E xt e rna l R e c e iv e r
60
0
50 40
60
30 20
120
10 0 0
15
30
45
60
75
90
This menu is used to specify collector cross-section, receiver dimensions and heat transfer characteristics, and desired field arrangement. This data can be selected from a library of built-in collectors, and/or be edited directly.
180
A l t i t ud e A ng l e, d eg
Tabulated optical efficiency as a function of solar zenith (1-altitude) and azimuth angles. Efficiency maps produced by any optical design program such as HFCAL, and even SAM can be entered to represent a particular field. Several built-in towers are available if no data are available.
“ s e e ”t hec av i t y .Thes i z eoft he reflector field, the height of the tower structure, and the cavity area are output from design based on thermal demand required of the tower given a solar condition and t het owe r ’ sopt i c alc har ac t e r i s t i c s . The fluid flows up to the receiver through the cold pipe, and returns through the hot pipe. The overall pressure drop from cold inlet to hot outlet is comprised of the frictional losses in the pipes and receiver, and the net gravity head between fluid column in the cold and hot pipes.
Heliostat field layout showing location of the tower is available on output. Land area required, number of heliostats, and tower structure height are included in the output reports.
THERMOFLOW 17
Rice Solar Energy Project
Solar Tower Power Plants
Nine solar thermal power plant projects were approved by the California Energy Commision in 2010 alone. As of mid-2011 a number of these are in construction in the southeastern California desert. Some of these projects utilize solar towers with molten salt and some use towers with direct steam generation and reheat in the receiver.
s t or age .Thi spr oj e c t ’ spl anwas submitted to the CEC by SolarReserve LLC and was approved by the CEC in December 2010. The model described here was created using publicly available information from the California Energy Commission website (http:// www.energy.ca.gov/sitingcases/ ricesolar/index.html).
tank through the receiver and returned to the hot tank. The solar boiler uses salt from the Output flow diagram shows to hot tank to produce a clear summer afternoon. He superheated steam from 30% more heat than required feedwater coming from is used to heat salt taken from the feedwater heating train, and to reheat steam from the turbine. Five feedheaters and a deaerator preheat the feedwater before it enters the solar boiler. The plant uses a dry cooling system (ACC) to condense low pressure steam to produce condensate. Use of an ACC minimizes water consumption, but penalizes the power cycle because the exhaust pressure is necessarily higher than it would be with a wet cooling system.
A THERMOFLEX model of Rice is shown below. The solar tower and boiler are on the left in the green When molten salt is used as the primary heat absorption fluid, it can box. The reheat steam turbine, feedwater heater train, and airbe stored in large atmosphericpressure tanks to provide capacity to cooled condenser system are shown on the right. Nominal performance ride-out cloudy periods, for load management, and power production is shown; the turbine generates about 150 MWe and the plant after sunset. exports 142 MWe, consuming about 8 MWe of auxiliary load to run the Rice Solar Energy Project The Rice Solar Energy Project is one ACC, pumps, and other loads. that uses molten salt with direct Molten salt is pumped from the cold 2 HP Steam
1837.1 p 950 T 285 m
1800 p 946.3 T 285 m
3 Hot Reheat 40 2
81.54 1049.4 680
42
29.15 1049 1862.9
29.15 548 1862.9
81.34 1049.4 1182.9
1
1 salt pump
48
Rice Solar Electric Plant
460.9 p 950 T 264 m
44
78.84 851.3 1182.9
78.84 851.4 1862.9
7 IPT-1
9
78.84 851.5 680
38
37.65 p 386.3 T 217.9 m 1230 h
176.3 p 710.3 T 11.56 m 1380.8 h
30
LPT-3
16
11.4 p 199.5 T 203.1 m 1141.5 h
37.65 p 386.3 T 14.07 m 1230 h
100 p 581.2 T 14.54 m 1320.2 h
34
36
G1
17
LPT-2
14 12
176.3 p 710.3 T 245.7 m 1380.8 h
296.6 p 839.7 T 11.43 m 1442.2 h
473.9 p 615.3 T 14.48 m
1844.7 p 624.4 T 285 m
IPT-3
10
6
473.9 p 615.3 T 264 m
15
LPT-1
IPT-2 296.6 p 839.7 T 257.3 m 1442.2 h
Cold Reheat 4
13
11
1.65 p 119.1 T 203.3 m 1034.3 h
19
11.4 p 199.5 T 14.85 m 1141.5 h
28
1.5 p 115.7 T 203.3 m
26
18
52
45
53.42 633.4 1862.9
460.1 p 611.8 T 14.48 m 1309.6 h
282.4 p 836.8 T 11.43 m 1441.2 h
37
35
167.9 p 707.5 T 11.56 m 1379.8 h
95.24 p 578.5 T 14.54 m 1319.2 h
36.73 p 383.9 T 14.07 m 1229 h
11.01 p 197.8 T 14.85 m 1140.5 h
39
25
46 29.15 548 1862.9 1886.4 p 458.6 T 285 m
33
1887.9 p 459 T 285 m
1895.4 p 416.9 T 285 m
29 1903.7 p 373.6 T 285 m
32 fe e d p u mp
Pa c k i ng e x h ASY
1844.7 p 615.4 T 285 m
Ex c es s s te am ASY
85 F 50 % 150047 kW 142458 kW 39.82 %
5 HPT
466.4 p 612.6 T 264 m
47
Ambient temp Ambient RH Gross power Net power Net electric eff.
150047 kW
450 p 947.5 T 264 m
8
43
The heliostat field is roughly circular with a 9000 foot (2750 m) diameter. At this size, the plant uses about 9 to 10 acre per nominal MWe capacity.
5.838 p 115.7 T 203.4 m 23
24
27
52
200.4 p 319.3 T 247.5 m
215.5 p 257.1 T 247.5 m
230.3 p 193.8 T 247.5 m
20 22
31
21 c o n d e n s a t...
243.6 p 117.1 T 203.3 m
Rice Solar Energy Project—design point heat balance. All data extracted from publically available sources, California Energy Commission. Solar tower with molten salt storage system and solar boiler shown on left in green shaded region. Reheat steam turbine with six feedwater heaters and an air cooled condenser (ACC) shown on the right side. Turbine capacity
18 THERMOFLOW
Ivanpah 1 SEGS
wer and storage system operation at 3:00 PM on re, the oversized solar collector absorbs about to run the turbine at full load. The excess energy the cold tank and stored in the hot tank. Ivanpah SEGS
Ivanpah SEGS will consist of two 100MWe blocks and one 200MWe block. The 100MWe blocks will use three towers to generate HP steam and one to reheat the steam. The 200MWe block will use four tower fields to generate HP steam and one to reheat the steam.
the cost and complexity of the molten salt loop, the storage tanks, the salt-to-water heat exchange system, and the charge of salt. However, it has no ability to store heat, and as such cannot make power unless the sun shines. The design does include a small gas fired boiler aid in plant startup and allow the plant to ride out transients due to temporary cloud cover. The use of gas backup is anticipated to result in a small amount of gas usage over the course of the year.
This design generates steam directly A THERMOFLEX model of this in the receiver. It thereby eliminates plant (shown below) was built using
publicly available information from the California Energy Commission website (www.energy.ca.gov/ sitingcases/ivanpah/index.html). In this model, the three HP tower fields are represented by a single icon on the left, and the single reheat tower is modeled by its own icon to the right. The tower blocks and relatively long piping runs are shown in the green area.
Ivanpah 1 SEGS—design point heat balance. All data extracted from the publically available California Energy Commission website. Solar tower field consists of three tower fields to generate high pressure steam from feedwater, and a separate reheat tower to heat cold steam exhausting from the HPT before readmission at the reheat turbine inlet. No storage system is included, but the plant includes a gas fired boiler to aid in plant startup and transient mitigation from passing clouds.
THERMOFLOW 19
Hybrid Solar-Fossil Power Plant
Model Overview
The overall heat balance result from a THERMOFLEX model of a proposed hybrid solar-fossil power plant is shown below. It is a condensing steam turbine power plant with an air-cooled condenser (ACC), a low pressure feedwater heater, and a deaerator. Steam is directly generated in a Linear Fresnel Collector (LFC) solar field and/or by a gas-fired package boiler installed in parallel. The solar field consists of three sections, one to preheat water, one to evaporate water, and the final section to superheat steam. The evaporator is designed to produce 30% quality steam. A steam drum separates the phases; liquid recirculates to evaporator inlet, and dry steam flows to the superheater field. Nominal turbine inlet conditions are 65 bar, 450 C, 13.6 kg/s. Nominal ACC pressure is 125 mbar in a 32 C ambient. This plant design minimizes plant makeup water requirements, consistent with desert-like site conditions present at many solar sites. Gross power
This model was used to simulate operation over a year using ambient and irradiance conditions typical of Daggett California, USA. The plant was run on a 24 hour schedule for 8000 hours per year. The annual average net LHV (lower heating value) efficiency was computed from the sums of net power produced and net fuel consumed; (GWhr electric export / GWhr LHV fuel consumption). Results of the yearly simulation show this relatively low efficiency steam cycle operates at 41% effective net LHV electric efficiency, a high value by Rankine cycle standards. This efficiency would be far higher if the plant were
shut down overnight, and would be lower in locations with poorer solar characteristics. Direct Steam Generation
THERMOFLEX can compute pressure drop and heat transfer for receiver tubes carrying single phase thermal oils, single phase water, two-phase water, and superheated steam. It includes a detailed physical model of thermal-hydraulic behavior of solar fields using Direct Steam Generation (DSG). Estimates of pressure gradient and heat transfer coefficient in twophase flow situations is more complicated than for single-phase situations. THERMOFLEX uses a one dimensional model where the flow path is discretized into a number of steps. The model estimates step-wise local values for internal heat transfer coefficient and pressure gradient based on prevailing flow conditions and physical characteristics of the flowpath including length, roughness and fittings. Condensing Steam Turbine
10954 kW 10260 kW 0.0002 kW 693.7 kW
Net power Net fuel input(LHV) Plant auxiliary
10954 kW G1 desup
35
HPT IPT
11
LPT
2
7
66.12 450 50.46 3294
66.12 450 48.75 3294
66.12 459.6 50 3318
M
Ov erf low by pass Superheater 12 69.65 285.5 50 2706
50 0.125 50.27 38.22 2332.7
39 66.12 450 0 3294
Ev aporator
BACKUP BOILER
Pac k age Boil er[20] - Bac k up Bl r: Aux
0 kW
42 76.04 181.1 0 771.1 41 84.94 181 50 771.1
ST Leak ASY
Recirc 16 79.38 281.1 50 1241.8
Economiser
13 0.8428 50.22 44.98 210.2
BFP
SOLAR FIELD
35 desup
20 THERMOFLOW
23 66.12 450 1.713 3294
ST Leak ASY
This design includes a natural-gas fired backup boiler, in parallel with the solar field, to generate steam when the field is unavailable due to maintenance, weather, or time-of-day. The backup boiler facilitates firm electric dispatch, without storage.
The steam cycle is small, does not include reheat and has few heaters. Therefore the base cycle efficiency is relatively low. However, this plant is also relatively simple, inexpensive, and easily capable of operation in full solar mode, full gas-fired mode, or in hybrid mode when some steam is generated in the field and the balance is provided by the fired boiler. So, it is flexible.
CND FWD
Direct Steam Generation (DSG) 0.8
ECO
25
EVA P
Mass Flux kg/m2-h .
20
0.6 0.5
15
0.4 10
0.3
of a desuperheater between the solar field and turbine.
Pressure distribution (below) is discontinuous because of pressure losses in piping systems between fields. The temperature plot is discontinuous between economizer and evaporator because subcooled economizer exit water mixes with saturated liquid recirculated back from the steam drum. The final steam temperature exceeds the turbine inlet by 10 C, requiring use 77
ECO
5 0.1
SUP
0.0
0 0
200
20
SUP
16
12
8
4
0 400
600
800
Position, m
distributions (above) are discontinuous in value because the mass flux in each field is different, to ensure reasonable velocities in each section. The slope of pressure gradient in evaporator is discontinuous because inlet water is slightly subcooled. The sharp discontinuity in value of heat transfer coefficient
EVA P
1000
Heat Trans Coeff kW/m2-K.
EVA P
400
600
Position, m
800
1000
between evaporator exit where steam quality is 30%, and superheater inlet illustrates how dramatically this differs between wet low quality steam and dry vapor. The number of paths in each field section is different, although the receiver tube diameters are the same throughout (70 mm OD). Therefore, the mass flux in each section is different, and the velocities are discontinuous at field boundaries. Velocity varies inversely with density along the flow path.
500
SUP
400
73
350 71 300 69
250
67
200
65
150 0
200
400
600
Position, m
800
1000
Temperature C .
450
75
Pressure bar .
0.2
The pressure gradient and heat transfer coefficient
Pressure Gradient mbar/m .
This series of three graphs show distributions of computed pressure, temperature, pressure gradient, heat transfer coefficient, mass flux, and bulk velocity from economizer inlet to superheater exit for this plant model operating 22 at design heat ECO balance 18 conditions. Three distinct 14 regions 10 correspond to the separate 6 fields for heating water, 2 making steam, 0 200 and superheating steam.
Bulk Velocity m/s .
0.7
THERMOFLEXout put si nc l udeabi r d’ s -eye view and a cross-section of the collector. Starting with Version 20, THERMOFLEX provides a 3D view of the solar field as shown here. This helps the user visualize effects of changing collector design, spacing, field arrangement, etc.
THERMOFLOW 21
Daily Plant Operation & Annual Yield
mode means the user specifies (or THERMOFLEX automatically Once a plant design is established, determines) equipment physical off-design simulations are used to characteristics, general compute expected plant configuration data, and desired performance at site and operating conditions expected during the year. thermodynamic constraints. THERMOFLEX computes the heat Typically simulations are done at different ambients, solar conditions, and mass balance and also determines the equipment size load levels, etc. Results are used to needed to realize the heat balance map expected plant performance e s ul t .I nc ont r as t ,“ of f -de s i g n” throughout the operating envelope, r mode means the equipment size is and to compute yearly totals for already established by a design power production, fuel calculation (subject to user edits), consumption, water consumption, and the model computes how etc. Sometimes off-design equipment of that size operates at simulations identify ways to fineuser-specified loading, ambient, and tune the original design so it more solar conditions. effectively satisfies expected duty cycle. In both modes the computed heat and mass balance parameters are THERMOFLEX models can run in design mode, in off-design mode, or the same, but the method of computing them is different. in mixed mode where some Off-design Modeling
in normal Excel cells, and computed results are stored in associated cells. The inputs and outputs are treated like any other Excel cell so they can be used in formulae, as source data for charts and tables, or linked to other Excel-aware applications. With E-LINK, any number of model runs can be made in a workbook. So, E-LINK is the tool to use for making annual yield calculations where some users make 8760 simulations to map out the year. Daily Operation
This example uses the hybrid solarfossil plant with DSG described on the previous page. During the day the solar and ambient conditions change. Prevailing values for these key model inputs are used to predict hourly plant operation. In this model, automated plant loading is components are in design and some accomplished using a steam flow E-LINK—Running in off-design. controller icon. This logical THERMOFLEX from Excel component is connected upstream of Wi t hThe r mof l ows of t war e ,“ de s i gn” E-LINK allows Thermoflow models the steam turbine and regulates to be run from steam flow to the turbine so it stays inside Microsoft in a specified range. When the solar Excel. E-LINK is a field makes less than the minimum feature included steam turbine admission flow, the with any controller automatically draws Thermoflow steam from the backup boiler to software license. makeup the shortfall. If the solar E-LINK is a great field makes more than the maximum tool for parametric admission flow, the controller shuts studies, performing down the auxiliary boiler and dumps batch runs, and excess steam to the condenser making automated through a letdown station. The calculations. c ont r ol l e r ’ sl i mi t sma i nt ai ns t e am Values for userturbine power between roughly 8 E-LINK workbook used to simulate hour-by-hour performselected model and 11 MW. ance throughout the year. Each column (case) represents inputs are entered one hour. Model inputs are in the yellow region, and computed model results are stored in the blue region. Other cells are normal Excel cells, available for use as needed. 22 THERMOFLOW
Off-design Modeling
Daily & Seasonal Variation of Ambient Temperature & DNI 900 750
- Summer -
35
600 25 - Spring / Fall -
450
15 300 5
DNI, W/sq.m.
150
- Winter -
-5
0 0
3
6
9
12 15 Solar Hour of Day
18
Annual Yield Simulations
Hour-by-hour simulations are used to compute annualized totals and averages. In this example the plant model is the hybrid solar-fossil power plant described on the previous page. It is operated on a 24-hour schedule with power levels ranging from just over 8 MW to a maximum of 11 MW. Power limits are established by limiting steam turbine admission flow in a range of 40 to 53.4 t/h.
21
24
condenser performance, and hence steam turbine power production. DNI (dashed lines) and solar angles vary with solar hour and day of year. These parameters strongly influence steam production in the solar field. The solar angles, not shown, are computed by the program for this location based on the day and the solar hour.
Hour-by-hour simulation results for winter, spring/fall, and summer Here, the hourly inputs and outputs days are plotted below. Steam turbine flow from the solar field is for three particular days are shown shown with bright green bars. Flow to demonstrate how the plant operates under different conditions. from the backup fossil-boiler is Estimated ambient temperature and shown with light green bars. Steam DNI for particular summer, winter, flows are plotted on the left axis in and shoulder season days are shown tonne/hour (t/h). Net plant power in the plot above. The ambient data (MW) is plotted as a solid black line on the right-hand axis. is from a model of the site in southwestern US, near the Kramer The solar field cannot make the Junction SEGS plants. The DNI is minimum admission flow at any estimated by the program using its hour of the winter day. For six theoretical sun model. hours in the middle of the day the solar field can make about 45% of Summer conditions are shown in the steam needed to load the turbine red, winter in blue, and shoulder at the minimum power. Throughout season in green. The solid lines the winter day the plant generates a show ambient temperature which roughly constant power level has a strong impact on air cooled W inter Day
On the summer day the solar field makes more steam than the turbine can swallow for six hours, and makes all needed steam for eight hours in the middle of the day. During early morning and late afternoon the field can still generate a significant fraction of maximum steam for the turbine. Plant net power varies throughout the day. The variation is most pronounced in the summer and shoulder season. This variation is the result of two effects. First, the admission steam flow varies throughout the day. Increased steam flow to the turbine raises its output power. Second, the air c ool e dc onde ns e r ’ sc apac i t yv ar i e s throughout the day. During the hottest parts of the day, the capacity is reduced which in turn reduces steam turbine gross power. The model accounts for these effects automatically, consistent with plant equipment capacity.
Shoulder Season Day
60
Steam Flow to Turbine, t/h .
associated with minimum steam flow to the turbine.
Summer Day 12
Backup Boiler Solar Field Net Power
50
10
40 30
8
20 6 10 0
Plant Net Power, MW
Ambient Temperature, C .
45
4 0.5
4.5
8.5
12.5 Solar Hour
16.5
20.5
0.5
4.5
8.5
12.5 Solar Hour
16.5
20.5
0.5
4.5
8.5
12.5 Solar Hour
16.5
20.5
THERMOFLOW 23
St ar t i ngi n1987wi t hi t sf l agshi ppr ogr am GTPRO™,Ther mof l ow’ ssof t war esui t ehasgr ownt oi ncl udeseven powerful, yet easy-to-use tools to analyze the spectrum of power generating technologies in use today, and underconsi der at i ont omeett omor r ow’ sdemandi ngchal l enges. As of 2012, Thermoflow has sold over 7500 program licenses to companies in more than 80 countries. This pr ovent r ackr ecor dmakesTher mof l ow’ ssof t war esui t et hemostwi del y-used, and well-respected in the power generation industry. A complete list of Thermoflow customers is available at www.thermoflow.com. A small sampling is listed below. ☼ MAN Solar Power Group ☼ eSolar ☼ E.ON Engineering ☼ NEM ☼ NOVATEC Solar ☼ Siemens ☼ ☼ Lahmeyer International ☼ Electricite de France ☼ SUEZ Tractebel ☼ Fraunhofer ISE ☼ ☼ Siemens CSP (Solel) ☼ Office National de l'Electricite (ONE) ☼ Renewable Energy Systems (RES) ☼ ☼ Lockheed Martin ☼ Ecolaire Espana ☼ Bechtel Power ☼ Black & Veatch ☼ ☼ Kraftanlagen Muenchen ☼ Chiyoda ☼ Duke ☼ Fluor ☼ Hyundai ☼ PB Power ☼ Stone & Webster ☼ ☼ Toyo ☼ TransCanada Power ☼ ALSTOM ☼ CMI Boilers ☼ Hangzhou Boiler ☼ Foster Wheeler ☼ ☼ General Electric ☼ Kawasaki ☼ Harbin Turbine ☼ Mitsubishi ☼ Rolls-Royce ☼ Solar Turbines ☼ ☼ Dong Fang Turbines ☼ Akzo ☼ BP ☼ British Energy ☼ Chevron ☼ ConocoPhillips ☼ ExxonMobil ☼ ☼ Tokyo Gas ☼ Total S.A. ☼ TransAlta Energy ☼ MIT ☼ China TPRI ☼ Korea EPRI ☼ Taiwan Power ☼ Univ. di Bologna ☼ Univ. of Calgary ☼ Univ. di Firenze ☼ Cobra Energia ☼ Iberdrola ☼ ☼ FERA Srl ☼ Veolia Energy ☼ Fotowatio ☼ TSK-INGEMAS ☼ ... ...and hundreds more at www.thermoflow.com
Thermoflow, Inc. 2 Willow Street—Suite 100 · Southborough, MA 01745 · USA ·
[email protected] · +1 508-303-5033
Thermoflow Europe GmbH Gartenstrasse 18, D-35469 Allendorf · GERMANY ·
[email protected] · +49 640-790-6991
24 THERMOFLOW August 2012
www.thermoflow.com
