All about compliance06 February 2024

A high percentage of manufacturing and process facilities will have plant that falls within the MCPD remit

Operations engineers responsible for mid-sized boiler plant are facing a flurry of forthcoming regulatory deadlines. So, what needs doing and by when?

Although some are well aware of the medium combustion plant directive (MCPD), which sets out to regulate the fuel combustion emissions of plant with a rated net thermal input of 1-50MW, many have some catching up to do. This is despite the European Union first mooting the MCPD over a decade ago.

“It’s been almost 10 years since the EU began stepping up its efforts to devise a directive that reduces emissions from all sorts of industrial activities,” explains Paul Whitehead, general manager of the Combustion Engineering Association (CEA). “Combustion plant soon came into the spotlight. It began with a directive for large plant of 50MW net thermal input or more, with the MCPD following on.”

The MCPD applies to all types of plant, including steam boilers and hot water boilers, burning any kind of fuel, be it gas, coal, oil or biomass. A high percentage of manufacturing and process facilities will have plant that falls within the MCPD remit, a directive that looks to control the harmful emission of particles such as nitrogen oxide (NOx).

To better gauge the size of plant that falls within the MCPD’s scope and draw a correlation between input and output, a 1MW steam boiler produces about 1,350kg of steam per hour, while a 5 MW steam boiler generates around 6,780kg. It is important to understand which boilers fall within the MCPD catchment because deadlines are fast approaching.

Although the deadline for new boiler plant passed in December 2018, a raft of cut-off dates are edging into view for existing systems. In fact, it may come as a shock to some that the deadline for registering existing boilers above 5MW and obtaining a permit passed in January 2024.

“One of the main problems is that no one really knows how many boilers are operating within the UK,” explains Whitehead. “Estimates put the figure at a few tens of thousands, but it’s a best guess. So, if we don’t know how many there are, or precisely where they are, and the people who have them don’t know they need a permit, you have a major education exercise on your hands. We support the MCPD as a good idea, but it requires managing, and needs resources to publicise the directive and process `the permits.”

Registering and permitting a boiler requires completing an application form and paying a fee to the relevant environmental agency, either the Environment Agency (England), Scottish Environment Protection Agency, Natural Resources Wales or Northern Ireland Environment Agency. Although the MCPD applies across the UK, the process differs slightly in each of the four nations. All applications undergo an assessment to ascertain if the boiler is permit-worthy, and if so, whether the permit should feature any associated rules or stipulations. The information required to submit an application includes: type of plant, what fuel it burns, running hours, output levels and whether a proper management system is in place.

“Location is also part of the assessment,” states Whitehead. “A sizeable boiler running a not-so-clean fuel close to a school might prompt the EA to contact the local authority for comment. Some local authorities have tighter limits than those set out by the MCPD. It’s quite an exacting process in many respects.”

The next deadline looming large is January 2025, when existing 5-50MW boiler operators must comply with specified emission limit values (ELVs). NOx limits are set at 200mg/m3 on gas and 200mg/m3 on gas-oil. Permit holders must measure their boiler emissions and make sure they comply. If not, corrective action must take place before the deadline.


Timely intervention is necessary because the regulator can require the boiler operator to suspend plant operations if it fails to comply with ELVs and causes significant damage to air quality. If non-compliance continues, the regulator may take enforcement action.

“In general terms, the limits set out by the MCPD are not excessively onerous for the UK because we predominantly burn natural gas, along with a little light oil and biomass,” says Whitehead. “Most will be able to comply, although there will be a few exceptions.”

By way of example, some of the limits could prove a challenge for those running reverse-flame steam boilers, as NOx is primarily a function of flame temperature. Flame temperature tends to be higher in boilers of this type. So what are the options for those facing such a scenario?

“Anyone operating reverse-flame boilers might have to down-rate the boiler or turn the burner down in order to comply,” he suggests. “Alternatively, you could approach a UK burner manufacturer for advice about technologies such as low-NOx burners or reduced NOx flame control. In such cases, any specified solutions will lead to a cost. Some retrofit solutions might cost £10,000 to £20,000, for example, while a major plant reinstallation may be £50,000 to £100,000. Sadly, this will come as a shock to many who either don’t know or don’t want to know about the MCPD.”

Low NOx burners control fuel and air mixing at each burner in order to create larger and more ‘branched’ flames. Peak flame temperature thereby reduces, resulting in less NOx formation. Regarding reduced NOx flame control, injecting a small amount of water or steam into the immediate vicinity of the flame will lower its temperature and reduce local oxygen concentration, subsequently decreasing the formation of thermal and fuel-bound NOx.

Even small boilers are subject to the MCPD, although operators of systems from one to 5MW net thermal input have a few more years: until January 2029 to register and get a permit; and until January 2030 to comply with ELVs.

“That’s where the bulk of the work lies,” concludes Whitehead. “I think environment agencies are now building up to what lies ahead in the coming years. Thousands and thousands of boilers to register and permit.”


Among the current MCPD anomalies is the hire boiler market. The Combustion Engineering Association (CEA) has some members that rent steam boilers, with estimates suggesting there are more than 600 such boilers in use across the UK.

“If you have a boiler exposed to poorly managed water and it needs a repair, it’s going to be offline for a month due to the lengthy process involved: cool down, drain down, inspection, welding, X-rays, refilling, re-inspecting and re-commissioning,” explains Paul Whitehead, general manager of the CEA.

“In these situations the common response is to obtain a hire boiler. However, if it’s a new model built after 2018, which it almost certainly will be, it requires a permit. At present we simply don’t know who has responsibility for that. The company which owns the boiler is not the boiler operator. Sure enough, the boiler might be certified, emissions tested and meet all regulations for pressure systems, but NOx emissions relates to operation: it’s the user’s fuel, water and location. There is limited information available at present regarding permits for hire boilers.”

For now, it seems the Environment Agency is aware of the situation and is developing plans to address it in the near future.

Steed Webzell

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Combustion Engineering Association

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