Managing Calorific Value and Health & Safety at Energy from Waste Facilities

Energy from Waste (EfW) facilities face a challenge that many people outside the industry don't realise: the waste arriving at the gate is getting "hotter". The calorific value (CV) of residual waste is rising, and operators are having to find creative ways to keep their furnaces within design limits. Some of those methods bring new health and safety risks that need careful management.

What is calorific value and why does it matter?

Calorific value is the amount of energy released when waste burns. Every EfW plant is designed around a CV range. As a guide, the calorific value of mixed municipal waste typically sits between about 7.5 and 11 MJ/kg.

When the CV runs too high, the furnace reaches its thermal limit before it reaches its tonnage limit. In other words, the plant can burn fewer tonnes of waste. That hits the business directly, because taking in high-heat materials like plastics and paper reduces how much waste a plant can process, and most revenue comes from gate fees.

A high CV can also mean higher grate and boiler temperatures, more slagging and fouling, more wear on refractory, and more unplanned shutdowns.

Why is CV rising?

The main driver is plastic. Plastics push calorific value up because of their high carbon content. Some common plastics carry huge amounts of energy: polypropylene and polyethylene average around 45 MJ/kg, compared with about 18.5 MJ/kg for PVC.

At the same time, the wet, low-energy fraction of the waste stream is being taken out. With separate food waste collections now required across England under Simpler Recycling, less wet organic material ends up in residual waste. Kitchen waste has roughly 40% moisture and a low CV of around 10 MJ/kg, so removing it naturally drives the CV of what's left upwards.

How operators are bringing the CV down

Across the sector, operators are using a range of approaches:

Adding sludge or wet waste. Some facilities co-feed sewage sludge or other wet material to dilute the energy content. De-watered sludge has a very low CV, averaging around 2.5 to 3.5 MJ/kg. However, getting the blend right is critical. Research on full-scale plants suggests a blending ratio of about 7% sludge, as going higher risks diluting the CV so much that combustion becomes incomplete. Sludge moisture above 40% can also substantially increase CO emissions.

Adding water or waste water. Some sites spray water or add waste water to the feed or bunker to absorb heat through evaporation.

Chemical additives. Some operators have added chemicals to bring the CV down or manage combustion. This must be approached with great care, both for combustion performance and for the health and safety of the people handling them.

Better bunker management. Skilled crane operators mixing high and low CV waste in the bunker remains one of the simplest and most effective controls.

Reducing throughput or adjusting combustion. Lowering the feed rate, controlling combustion air, and using flue gas recirculation can all help, though reducing throughput costs money.

Managing waste acceptance. Reviewing supply contracts and waste acceptance criteria helps control what arrives in the first place.

The health and safety risks you can't ignore

Every one of these methods changes how the site operates, and every change brings risk. Here's what operators need to think about:

Permit compliance. Your Environmental Permit lists the waste types (EWC codes) you're allowed to accept and the activities you can carry out. Bringing in sludge, waste water or chemical additives may need a permit variation. Check with the Environment Agency before you start, not after.

COSHH. Any chemical additive needs a full COSHH assessment covering storage, handling, PPE, spill response, and how it behaves at combustion temperatures.

Sludge and waste water hazards. Sludge can release hydrogen sulphide and carry bioaerosols and pathogens. Tanks, pits and reception areas may be confined spaces. Wet material also increases slip risks across the tipping hall.

DSEAR. Dusts, flammable vapours and gases from some wastes and additives may create explosive atmospheres that need a DSEAR assessment.

Fire risk in the bunker. High CV waste, particularly plastics and lithium batteries hidden in residual waste, increases the risk of bunker fires. Your fire risk assessment, detection, suppression and emergency plans need to reflect the waste you're actually receiving today, not what you received when the plant was built.

Management of change. Any change to feedstock or process should go through a formal management of change process, with updated risk assessments, method statements and staff training.

Training. Crane operators, tipping hall staff and control room teams all need to understand the risks of new materials and what to do when things go wrong.

How Safety First can help

At Safety First, we support waste and EfW operators across the UK with practical, site-based health, safety and environmental compliance. Our services include fire risk assessments, DSEAR assessments, COSHH assessments, workplace inspections and compliance audits, accident and incident investigation, environmental compliance audits, EA permit applications, and WAMITAB/TCM support for waste sites.

If your site is changing how it manages calorific value, or you're simply not sure your risk assessments still reflect the waste coming through your gate, get in touch with us for a no-obligation conversation.