The Component CHP
The CHP component represents a combined heat and power plant or other cogeneration component in which Heat (no Steam) and Electricity are generated from Fuel as by-products.
Component Template
The component template CHP.e-ctpl is located in the Component template library folder Combined Generation.
Integration Into a Scheme
The following figure from tutorial 06 shows as an example how to integrate the component into a scheme.
Operating Principle
Please note the important information on the material model and the insertion of the pins in the article Fuel Special Features. The component converts the energy contained in the fuel into electricity and heat by combustion. The energy that does not leave the component either in the form of electricity or heat is added to the exhaust gas stream.
The conversion efficiencies are specified in the component. The direct input of the Nominal Thermal Efficiency or the specification of the Nominal Thermal Capacity is possible. Furthermore, a part load behavior can be added via characteristic curves.
Calculation of Efficiencies at Full Load
Efficiencies at full load are determined either by directly entering the Nominal Thermal and Electrical Efficiency (ref. NCV) or by specifying the Nominal Thermal Capacity and Fuel Demand (NCV) at Nominal Operation (nominal fuel power). The fuel power and all efficiencies are always related to the net calorific value – NCV (lower heating value) of the fuel. If the option Enter Characteristic Curve (absolute values) is selected for the Part Load Performance, the rated outputs are determined directly from the characteristic curves.
If the plant is able to utilize the calorific value of the fuel, an efficiency of over 100 % can be entered. However, this is not included in the calculation of the exhaust gas temperature. Because the condensation of the water in the exhaust gas is not included in the calculation, very low exhaust gas temperatures occur in this case. This only has a negative effect on the result if heat is extracted again from the exhaust gas in a heat exchanger. Otherwise the resulting error messages can be ignored.
Part Load Behavior
There are three different options for specifying the Part Load Performance. The default setting is a Constant Efficiency in Part Load. If the Part Load Performance deviates from this, the specification of absolute values is recommended in most cases.
If Constant Efficiency in Part Load is selected, either the Nominal Efficiencies (\(\eta_{el}\), \(\eta_{th}\)) are entered directly and the Nominal Capacities are determined from them, or the Nominal Capacities (\(P_{el\ n}, \dot{Q}_{th\ N}, \dot{m}_{fuel\ n} NCV\)) are entered, from which the Efficiencies are then calculated:
\(P_{el\ n}=\eta_{el} \dot{m}_{fuel\ n} NCV\),
\(\dot{Q}_{th\ n}=\eta_{th} \dot{m}_{fuel\ n} NCV\).
These are then constant over the entire operating range of the component:
\(P_{el}=\eta_{el} \dot{m}_{fuel} NCV\),
\(\dot{Q}_{th}=\eta_{th} \dot{m}_{fuel} NCV\).
If Enter Characteristic Curve (absolute values) is selected, the relationship between Thermal Power \(\dot{Q}_{th}\), Electrical Power \(P_{el}\), and Fuel Power \(\dot{m}_{fuel} NCV\) is established directly via two characteristic curves \((f_{el\ abs}\), \(f_{th, abs})\). Because absolute power ratings are specified with these characteristic curves, an additional specification of the nominal power ratings or the minimum part load is not necessary:
\(P_{el}=f_{el\ abs}(\dot{m} NCV)\),
\(\dot{Q}_{th}=f_{th\ abs}(\dot{m} NCV)\).
As an example, the following screenshot shows the specification of the part load for a CHP unit with 70 kW rated electrical output, 100 kW rated thermal output and 200 kW rated fuel output. The minimum part load is 50 % and the efficiencies at part load are worse than the nominal efficiencies.
If Enter Characteristic Curve (relative to nominal point) is selected, the relationship between thermal power \(\dot{Q}_{th}\), electrical power \(P_{el}\), and fuel power \(\dot{m}_{fuel} NCV\) is established via two characteristic curves. These characteristic curves represent the relationship between the relative part loads of the various forms of energy. In this case both the characteristic curves and the part load curves are required as input. The following formulas are used to calculate the part load behavior:
\(\frac{P_{el}}{P_{el\ n}}=f_{el\ rel}(\frac{\dot{m}_{fuel}}{\dot{m}_{fuel\ n}})\),
\(\frac{\dot{Q}_{th}}{\dot{Q}_{th\ n}}=f_{th\ rel}(\frac{\dot{m}_{fuel}}{\dot{m}_{fuel\ n}})\).
As an example, the following screenshot shows the specification of the part load for a CHP unit with 70 kW rated electrical output, 100 kW rated thermal output and 200 kW rated fuel output. The minimum part load is 50 % and the efficiencies at part load are worse than the nominal efficiencies. This input produces the same result as the input in the screenshot under Characteristic Curve (absolute values).
Minimum Load and Modulating Operation
A Minimum Part Load can always be specified when entering a Constant Efficiency in Part Load.
Additionally, the option Modulating Operation below Minimum Load can be activated with a check mark in the checkbox. If this option is selected, additional formlets for entering the Minimum Part Load appear when specifying the part load behavior via characteristic curves. Then observe the note: Please complete the part load diagram up to the value 0/0 according to the operating behavior during the clocking of the plant (intermitting operation).
Modulating operation means that the component can be switched on and off several times within one simulation time step. In this way it is possible to run part loads on average, which are below the minimum part load. A component with 100 kW nominal thermal power and a minimum part load of 50 % can generate 25 kW on average in one hour by generating 100 kW for 15 minutes and being switched off for 45 minutes.
If modulating operation is not allowed, the component cannot generate power below the minimum part load. In this case, it must be ensured that demands in these part load ranges can be covered by other plants or that energy can be dissipated so that the plant can be operated above the minimum part load.
Activating Modulating Operation means that the component can also run under Minimum Part Load. In this case the Operating Hours are less than in normal part load operation. In the case described above, the component has only 15 operating minutes within one hour.
Combustion Calculation
There are three different ways to calculate the Exhaust Gas Temperature and the exhaust gas mass flow. All three options are based on the assumption of complete combustion.
If the Air Ratio (\(\lambda\)) is entered, the minimum air quantity required for complete combustion is determined from the composition of the fuel. The minimum amount of air (\(\dot{n}_{O_2\ min}\)) results from the composition of the fuel as follows:
\(\dot{n}_{O_2\ min} = \dot{n}_{fuel} ( 2 x_C+\frac{1}{2} x_H + 2 x_S -x_O ) \).
From this follows the actually required amount of air (\(\dot{n}_{O_2}\)) by multiplication with the air ratio:
\(\dot{n}_{O_2}=\lambda \dot{n}_{O_2\ min} \).
The composition of the exhaust air can be determined from the mass flow rate of the fresh air (\(fa\)) and the fuel quantity and composition, taking into account the ash content. This then results in the specific heat capacity of the exhaust gas (\(\dot{H}_{eg\ out}\)):
\(\dot{H}_{eg\ out}-\dot{H}_{fa\ in} = \dot{m}_{fuel} NCV – P_{el} – \dot{Q}_{th}\).
This in turn gives the temperature of the exhaust gas.
If a constant air mass flow rate is specified, the calculation is carried out analogously to the specification of the air ratio. In this case, however, the air ratio is determined from the supplied mass flow (or substance flow rate) and the minimum oxygen demand and not vice versa. Otherwise, the calculation is carried out analogously via the energy balance and the specific heat capacity of the exhaust gas.
If an Estimated Exhaust Gas Temperature is given, the exhaust gas mass flow rate and air ratio are calculated using a fixed value for the specific heat capacity of the exhaust gas. This amounts to \(1.045 \frac{kJ}{kg K}\). The calculation is otherwise analogous to the calculation under Air Ratio.
Specification of the Outlet Temperature
As in all components of heat networks, the Flow Temperature (outlet temperature) must also be specified for this component. This is used to calculate mixing temperatures after optimizing the energy balance. This behavior is described in this article.
Operating and Full Load Hours
The Full Load Hours are calculated based on the Nominal Electrical Capacity. They are output as a time series. Each value in the time series is the part load in relation to the nominal electrical capacity. Converted into the unit h/a, this results in the number of full load hours. 75 % part load at a given time therefore means that 0.75 full load hours per hour occurred at that time. If this load condition is operated all year round, the result is 6570 full load hours per year (h/a).
Economic Data
The following tables show the investment costs of CHP, determined on the basis of data of the ASUE Arbeitsgemeinschaft für sparsamen und umweltfreundlichen Energieverbrauch e. V. (BHKW-Kenndaten 2014/2015. Module, Anbieter, Kosten, Berlin 2014) and the Danish Energy Agency (Technology Data catalogues, 2024).
Natural Gas
| Electrical nominal capacity (kW) | Investment costs including installation (EUR/kW) | Investment costs including installation (EUR) | Investment costs (EUR) | Specific investment costs (EUR/kW) |
|---|---|---|---|---|
| 1 | 15 240 | 15 240 | 9 585 | 9 585 |
| 4 | 6 827 | 27 309 | 18 086 | 4 521 |
| 11 | 3 398 | 37 383 | 25 781 | 2 344 |
| 101 | 1 466 | 148 115 | 98 089 | 971 |
| 351 | 998 | 350 186 | 218 866 | 624 |
| 501 | 913 | 457 529 | 275 620 | 550 |
| 751 | 830 | 623 420 | 358 287 | 477 |
| 1001 | 810 | 811 074 | 415 936 | 416 |
| 1501 | 731 | 1 097 246 | 619 913 | 413 |
| 5001 | 657 | 3 286 098 | 2 028 456 | 406 |
Biogas
| Electrical nominal capacity (kW) | Investment costs including installation (EUR/kW) | Investment costs including installation (EUR) | Investment costs (EUR) | Specific investment costs (EUR/kW) |
|---|---|---|---|---|
| 11 | 4 521 | 49 732 | 34 298 | 3 118 |
| 101 | 1 441 | 145 524 | 96 373 | 954 |
| 351 | 1 018 | 357 470 | 223 419 | 637 |
| 501 | 941 | 471 560 | 284 072 | 567 |
| 751 | 865 | 649 594 | 373 330 | 497 |
| 1001 | 869 | 869 887 | 446 096 | 446 |
| 1501 | 752 | 1 129 180 | 637 955 | 425 |
| 5001 | 598 | 2 991 037 | 1 846 319 | 369 |
Sewage Gas
| Electrical nominal capacity (kW) | Investment costs including installation (EUR/kW) | Investment costs including installation (EUR) | Investment costs (EUR) | Specific investment costs (EUR/kW) |
|---|---|---|---|---|
| 11 | 4 931 | 54 246 | 37 411 | 3 401 |
| 101 | 1 481 | 149 553 | 99 042 | 980 |
| 351 | 1 040 | 365 091 | 228 182 | 650 |
| 501 | 960 | 480 749 | 289 608 | 578 |
| 751 | 880 | 660 923 | 379 841 | 505 |
| 1001 | 871 | 871 507 | 446 926 | 446 |
| 1501 | 756 | 1 134 494 | 640 957 | 427 |
Liquefied Petroleum Gas
| Electrical nominal capacity (kW) | Investment costs including installation (EUR/kW) | Investment costs including installation (EUR) | Investment costs (EUR) | Specific investment costs (EUR/kW) |
|---|---|---|---|---|
| 1 | 16 496 | 16 496 | 10 375 | 10 375 |
| 4 | 6 819 | 27 277 | 18 064 | 4 516 |
| 11 | 3 388 | 37 266 | 25 700 | 2 336 |
| 101 | 1 510 | 152 502 | 100 995 | 1 000 |
Wood Chips
| Electrical nominal capacity (kW) | Investment costs including installation (EUR/kW) | Investment costs including installation (EUR) | Investment costs (EUR) | Specific investment costs (EUR/kW) |
|---|---|---|---|---|
| 23 860 | 3 573 | 85 250 265 | 57 087 164 | 2 393 |
| 100 000 | 3 600 | 360 000 000 | ||
| 200 000 | 3 575 | 715 000 000 |
Heating Oil
| Electrical nominal capacity (kW) | Investment costs including installation (EUR/kW) | Investment costs including installation (EUR) | Investment costs (EUR) | Specific investment costs (EUR/kW) |
|---|---|---|---|---|
| 1 | 19 609 | 19 609 | 12 333 | 12 333 |
| 4 | 6 512 | 26 046 | 17 249 | 4 312 |
| 11 | 2 332 | 25 651 | 17 690 | 1 608 |
