Combined Heat & Power (CHP) and Air Quality – The new draft London Plan

The release of the draft new London Plan contains a number of significant and ambitious energy policy changes from the existing London Plan. In particular, the future of Combined Heat and Power (CHP) as the go-to energy source for communal heating is now unclear.

The role of CHP has been subject to a very clear demotion in the communal heating hierarchy in Policy S13 Energy Infrastructure. In the supporting text, the following statement is also made:

‘Further evidence about the relevance of CHP ..will also be provided in the Energy Planning Guidance document..However, it is not expected that gas engine CHP will be able to meet the standards required within areas exceeding air quality limits with the technology that is currently available.’

The principal source of poor local air quality in London are oxides of nitrogen (NO_x). However, there are several established and very effective technical solutions available for the treatment of NO_x emissions from gas CHP plant.

In terms of current requirements, the Sustainable Design and Construction SPG (2014) recommends the application of a 95mg/Nm³ limit across most of London for gas CHP. This figure is achievable with the use of a ‘3-way catalyst’ on smaller CHP engines, and Selective Catalytic Reduction (SCR) technology on larger ones. Both processes involve passing the exhaust gases over a catalyst in order to convert NOx into less harmful products such as nitrogen and water, with SCR also requiring the addition of a chemical reagent into the process, usually urea.

Both technologies enable a reduction in NOx emissions from gas CHP engines to at least 50mg/Nm³, with SCR able to go even further to below 25mg/Nm³. It is therefore not yet clear what air quality standards can be set within the new London Plan which will make the application of gas CHP engines on air quality grounds unfeasible.

In addition to this, the London Environment Strategy (released May 2018) appears to row back from the strong statement made within the new draft London Plan on the application of CHP. The following is stated:

‘Where there remains a strategic case for combustion based CHP systems on very large heat networks, these will continue to be considered on a case by case basis..’

There is consequently a great deal of confusion on the GLA’s proposed approach to CHP. It is very much a case of watch this space.