Technology Overview

Combined heat and power (CHP) is the simultaneous generation of usable heat and power (usually electricity) in a single process. The electricity is generated on or close to your site, allowing you to capture and use the resulting waste heat for site applications .

How CHP Works

At the heart of a CHP installation is something called the ‘prime mover’ (heat engine). This is the equipment in a CHP system that provides the motive power to drive the electrical generator and produces the heat. It is generally a gas turbine, steam turbine or internal combustion engine.

The different types of prime mover available mean that CHP can use a variety of fuels and provide for various heat demands – either in the form of hot water or steam. As such, CHP is very flexible and can be tailored to the requirements of each site.  It can be used across a wide range of sectors and can provide cost-effective energy solutions for large and small energy users alike.

How Does it Save Energy?

CHP makes more efficient use of primary fuel for producing heat and power than separate conventional methods, i.e. on-site boilers and power stations. That means it can deliver significant environmental benefits and cost savings, given the right balance of technical and financial conditions.

Figure 1: Energy savings through typical new small-scale packaged CHP compared to conventional sources of heat and power generation (shown in units of energy)

This is illustrated in Figure 1, which shows that the UK average fossil fuel electricity generator has an efficiency of around 40%. The remaining 60% of the energy is lost, mostly as heat via cooling towers and to a smaller degree in electricity transmission. Packaged CHP that is correctly sized and designed can have an overall conversion efficiency of primary fuel to usable energy   (power and heat) of around 75%.

Is CHP Proven?

There are 1,438 CHP schemes in operation in the UK. Of these, 328 are in the industrial sectors and 1,110 are in commercial, public administration, residential, transport and agriculture sectors.

Source: Carbon Trust, Introducing combined heat and power, 2010

Packaged CHP

Packaged CHP systems, typically ranging from 60kWe to 1.5MWe, are designed and supplied as complete units, selected to meet the requirements of the site and its energy demands. The package contains the engine, generator and heat recovery equipment, together with all the associated pipework, valves and controls.

The equipment is mounted on a steel structure and surrounded by an enclosure that reduces noise levels in the adjacent area. The enclosure normally contains a control panel that is accessible from outside the package. The package can also usually be easily dismantled to provide access for maintenance purposes. Figure 2 shows how a packaged CHP works.

Figure 2: A packaged internal combustion engine CHP

The prime mover for packaged CHP units is usually an internal combustion engine system. Heat is then recovered from the engine exhaust system and water jacket via suitable heat exchangers to provide a source of heat .

Biosus Gas CHP system examples.