Helping operators and local authorities to avoid smells and smoke from combustion plants

Helping operators and local authorities to avoid smells and smoke from combustion plants
16 February 2021

Helping operators and local authorities to avoid smells and smoke from combustion plants

Mark Broomfield and Tom Buckland explain how local authorities and plant operators can head off the growing air quality problems that sometimes result from combustion plants.

Good smells and bad smells
Fresh spices, the smell of baking bread, the sound of a baby chuckling – these are some of the most wonderful smells and sounds that we experience. A great tune or an evocative fragrance can take you back to a memory or a time of your life like nothing else. On the other hand, the noise of a generator starting up and the smell of diesel fumes or smoke wouldn’t make it onto many people’s list of their favourite smells and sounds. But, increasingly, the clanking and smells of a generator starting up are becoming a reality, particularly for people living and working in cities and commercial districts. Why is this a growing problem? And, how can local authorities and operators fulfil their obligations to make sure that noises and smells don’t cause a problem for neighbours?

Why is the use of generators on the increase?
One reason is that the electricity distribution networks need a reliable source of power to balance periods of high demand now that we are moving away (for excellent reasons) from fossil-fuel-fired power stations to a more distributed network with a wide mix of power sources. Sometimes, this balance is provided by clean sources of energy, such as wind or solar power, or by intensive users cutting their demand. But other ways of meeting this demand are also used – and one common solution is to use standby diesel or gas-fired generators that would otherwise be idle for most of the time.  

As a result, the situation arises where generators are running for more of the time, but still intermittently and unpredictably. This is just about the best possible way to produce amenity problems for the neighbours of these sites – stopping and starting generators often results in short-term smoke, odours or noise. Furthermore, using generators in this way can cause more frequent failures and operational problems. Neighbours of these sites probably won’t know when a generator is going to start running or how long for, which is likely to cause more annoyance.

Smells, smoke and noise are bad enough in themselves, but they can also have wider effects – for example, affecting property prices, and acting as a disincentive to new businesses and residents to move into an area that would otherwise be attractive.

What can we do about it?
To tackle these problems, the City of London Corporation contracted Ricardo to prepare guidance for operators of all kinds of combustion plant, backed up by two industry-focused webinars held in July and October 2020. The aim of these activities was to help inform plant designers and operators, as well as planners and environmental officers, at all stages of the process of designing and using combustion plant. Ricardo was very pleased to work with the team at City of London Corporation to develop and present this work.

The new guidance is available at the City of London Corporation website. Ruth Calderwood of City of London Corporation commented, “The webinars and guidance generated a lot of discussion and interest from partners across London and further afield.  The new materials will help us to minimise the impact of combustion plant on local air quality in City of London and beyond.”

One of the most important parts of the guidance is a simple two-page guide, which is packed with key points for avoiding air quality impacts. The recommended key points are shown in the table below (you can also find a pdf version at the City of London website). This is a very practical checklist that could be kept as part of an operating manual, taken to site by an inspector, passed on to residents or shared with developers applying for planning permission.

We hope this summary and the other resources available will be useful for operators, regulators and neighbours of combustion plant in the Square Mile, and in cities throughout the UK and beyond. Ricardo is very grateful to the City of London Corporation for funding this work, arranging the webinars, and for sharing the guidance through its website and social media presence.

If you are facing problems from combustion plant or would like to discuss other air quality issues that we may be able to assist with, please get in touch. You can also read about Ricardo’s wider air quality capabilities here, including an outline of our innovative approaches to managing urban air quality.

Key points

Key points for planning and equipment selection
KP1. Alternatives to combustion-based technologies are available and should be considered at the early stages of project development.
KP2. A range of combustion technologies are available, of which diesel fired generators are among the most polluting. These should be avoided if possible.
KP3. Different regulatory regimes apply to plant with different capacities, fuels, combustion technologies and proposed uses. This will affect the range of applicable controls and enforceable emissions limits.
KP4. Plant is designed to achieve different emissions levels and plant performance may degrade over time. It is important to select plant with appropriate emissions limits and assess potential impacts on a robust basis.
KP5. When selecting a contractor, its credentials, remote monitoring capabilities, helpline facilities, location of and ability to offer consistent engineers and charges, should be considered.
Key points for maintenance, service and testing
KP6. Maintenance and monitoring should be planned.
KP7. If testing causes problems, neighbours should be contacted to warn of upcoming tests, and identify the least disruptive times for testing to be carried out.
KP8. Tests may need to be scheduled to avoid periods of adverse weather conditions and/or high pollution levels.
KP9. Proper maintenance is vital to ensure the system functions well and does not suffer frequent outages.
KP10. Appropriate training for all operating staff (direct employees or contractors) should be undertaken, regardless of how much or how little involvement with operation they may have. 
KP11. Operators should be familiar with and follow the manufacturer’s guidance for the individual components of the system, including the generator/boiler itself, the flue system, power/ heat metering, fuel handling equipment, safety procedures, and lubrication of key components.
Key points for optimal management and operation
KP12. Standby and prime power diesel generators are usually optimised to run at 50-80% of total load rating. Natural gas generator sets, regardless of application and rating, are almost always optimised to run between 70-100% of total load rating.
KP13. Although systems are available for directly measuring the concentrations of emissions from combustion processes, emissions from smaller-scale generators or boilers/CHPs are normally monitored only indirectly via plant performance.
KP14. A remote monitoring and advisory service can help to achieve maximum performance and cost benefits.
Key points for flue heights and older/higher emitting plant
KP15. Screening tools such as the D1 guidance provide a valuable first step in specifying a minimum stack height, however it may not be possible to meet all requirements, which may be an indication that the combustion-based solution should be reconsidered.
KP16. There is potential for higher emissions of air pollutants from older plant than for modern plant which may be subject to a higher standard of emission controls – either through type-approval or environmental permits. 
KP17. It may be possible to retrofit an older plant with emissions abatement technology (e.g. particulate trap/ filter or a catalyst), where the chimney height is not adequate to disperse emissions, however this will depend on the engine type.
Key points for regulating combustion plant
KP18. An air quality assessment should be carried out to confirm compliance of any proposed combustion plant with requirements on location, stack height, emissions and the absence of significant air quality impacts.
KP19. Voluntary measures to minimise impacts on air quality may be at zero cost or low cost to the operator, and in some cases, improvements may result in an economic benefit – for example, resulting from improved plant efficiency or availability. 
KP20. Clean Air Act controls cannot be applied to combustion plant with an environmental permit (see below) but most permits include a provision regarding dark smoke; if dark smoke is an issue for such a plant then the appropriate regulator can be asked to intervene.
KP21. Prior to 2019, generator engines >560kW output were not subject to Non Road Mobile Machinery controls and consequently existing machines, if used as a stationary engine may be subject to the Medium Combustion Plant Regulations, and hence require a permit.