Technology

How does Waste to Energy work?

Residual waste, which is the waste left after any recyclable materials have been removed and recovered, is fed into a boiler. The heat that is generated through this process is used to power a steam turbine, generating electricity and heat.

Any ferrous and non-ferrous metals are extracted from the inert bottom ash which results from the combustion process.

The Incinerator Bottom Ash (IBA) can be recovered and recycled as a substitute for natural aggregate. Recycling IBA replaces the need to use non-renewable materials as aggregates and reduces the environmental impact of their extraction.

The Energy from Waste plant emissions are regulated through the Integrated Pollution Prevention and Control regime and are currently monitored by the Environment Agency. Emissions from the stack comply with the most stringent UK and European pollution control standards.

Air Pollution Control residues (APCr) – the residual ash remaining after stringent filtering and scrubbing is usually disposed of at hazardous waste landfill.

Construction of a Turn Key Plant

PMAC Energy are focused on using the most innovative and efficient technologies currently in use as part of our long-term strategy. The plant works by burning Municipal Solid Waste (MSW) to generate steam. The steam then drives a turbine to generate electricity. The technology used at the proposed plant will produce a substantial amount of electricity and enough energy to power 56,000 homes across the Teesside area.

As part of our combustion technology, PMAC Energy uses a reverse acting grate. Installed in 90% of the world’s energy recovery plants, combustion grates are the most tried and tested technique for heat recovery. Uniquely, the bars of the grate move in the opposite direction to the downward gravitational pull of the waste. This approach is not only a highly efficient method of mixing the combustible material, it also provides permanent protection of the underlying equipment – as it ensures there is a thick, insulating layer of waste covering the grate.

The embers at the top begin the combustion process of the waste as soon as it arrives on the grate, while the significant loss of pressure across the grate ensures there is a homogenous distribution of air during combustion.

The process is well-established, robust and long-lasting; and it can handle a variety of combustible materials with a wide range of net calorific values (NCVs):

Combustion is complete, despite the heterogeneous nature of the waste, with a low level of unburned material in the bottom ash
The amount of unburned CO-type gases is extremely low
Availability of the equipment is high, and its lifetime is long

Heat-recovery boilers

A heat-recovery boiler is integrated within the incinerator, which makes it possible to provide cooling for the incinerator itself, prevent obstructions from building up and avoid any loss of performance in the connecting ducts. Our boilers are designed to cope with the build-up of residues and the corrosive effects of flue gases produced by the thermal treatment of domestic waste.

Specifically, the boilers guarantee:

- high levels of thermal performance
- long-lasting heat exchange surfaces
- lengthy operating periods without the need for manual cleaning
- More information on heat-recovery boilers

Energy recovery

The particular type and characteristics of the thermal cycle all depend on the use for which the recovered energy is destined. Recovery can take the form of heat – to supply urban heating networks or steam for industrial use. It can also be transformed into electricity, which can be delivered externally – with a small amount of the electricity generated being retained for use by the plant itself. The ratio of these two different forms of energy can be modulated according to actual needs, seasons and times of day. This is known as cogeneration.

What does the future hold?

The recovery of energy from waste will play a significant role in both the waste management industry and the energy production industry for the foreseeable future.

With efforts to reduce plastic from packaging and variety of household products coming into force in the near future, emissions from ‘tried and tested’ Waste to Energy plants such as the one proposed by PMAC Energy could rival the promised (and as yet undelivered) results from Gasification processes.

More importantly, Waste to Energy plants look set to play a major role in the reduction of waste being transported to Landfill. The UK will soon have nowhere to dump its waste, with many landfills across the country reaching full capacity in the next several years.