Boiler
Introduction and Model¶
The boiler utilizes sewage gas from the biogas storage to heat the anaerobic digester and maintain its necessary operating temperature. It serves as a secondary heat generator that is only operated if the heat supply from the CHPs is insufficient.
The boiler is implemented as a black box model, as its internal workings are not considered critical and are too complex to model in detail. The thermal power generation is calculated with defined efficiencies at the current utilization of the boiler. The biogas consumption of the boiler is calculated with the current utilization and the lower heating value of the biogas. The utilization rate \(k_{load}\) of the boiler depends on the heat demand \(P_{th,demand}\) of the anaerobic digester and can vary between a defined minimum utilization of 30% and 100%. The following cases are assumed:
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High heat demand (\(P_{th,demand} \ge P_{th,max}\)): Boiler is used at maximum utilization (\(k_{load} = 1\))
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Partial heat demand (\(P_{th,min} \le P_{th,demand} \lt P_{th,max}\)): Boiler is partially utilized (\(0.30 \le k_{load} \lt 1\))
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Low heat demand (\(P_{th,demand} \lt P_{th,min}\)): Boiler is used at minimum utilization (\(k_{load} = 0.30\))
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No heat demand (\(P_{th,demand} = 0\)): Boiler is not utilized (\(k_{load} = 0\))
Equations¶
Thermal power¶
| Symbol | Description | Unit |
|---|---|---|
| \(P_{th}\) | Thermal power generation | kW |
| \(P_{th,max}\) | Maximum generation of thermal energy | kW |
| \(k_{load}\) | Utilization rate of the boiler | - |
| \(\eta_{th}(k_{load})\) | Thermal efficiency at current utilization rate \(k_{load}\) | - |
Biogas consumption¶
| Symbol | Description | Unit |
|---|---|---|
| \(\dot V_{gas}\) | Biogas consumption of the boiler | Nm3 \(\cdot\) h-1 |
| \(P_{th,max}\) | Maximum generation of thermal energy | kW |
| \(k_{load}\) | Utilization rate of the boiler | - |
| \(H_{u,gas}\) | Lower heating value of the biogas | kWh \(\cdot\) Nm-3 |
Source code documentation¶
mod boiler
mod boiler_init