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Biogas Boiler

One option for using the biogas produced by an AD system is to install a biogas boiler. This would offset some of the steam produced by a distillery’s current boiler, reducing fossil fuel use.


Biogas Boiler

The biogas boiler page of the tool calculates the capacity of boiler required in order to use all the available biogas, and calculates the resulting fuel bill saving. The tool also calculates the amount of subsidy available under the Renewable Heat Incentive (RHI), if the required boiler capacity does not exceed the scheme’s 200 kW threshold. Key inputs are:

  1. Thermal Efficiency: biogas has a lower calorific value than natural gas, and boiler efficiencies are generally lower. Information from suppliers suggests 80% is a typical value.
  2. Steam Requirement Factor: this is the proportion of time in a normal operating week during which steam is required – e.g. the proportion of time during which at least one still is running. It is used to calculate the required boiler capacity, and so a high level of accuracy is only necessary where the capacity may be close to the RHI threshold.
  3. Enthalpy of Feed Water/Steam: users who are interested in the mass of steam generated can adjust these inputs to reflect the steam requirements and boiler feed water temperatures of their distillery. As a default, it is assumed steam is required at a pressure of 8 bar. The economic results of the tool are calculated from kWh of steam produced, and so are not affected by changes here.
  4. Capital, Installation and Maintenance Costs:the tool provides an estimate of boiler capital cost based on the required capacity and information obtained from suppliers. Maintenance costs are assumed to be 5% of capital costs.