Exhaust Gas Heat Exchangers

A heat exchanger is a device for transferring heat energy from a liquid or gas, to another liquid or gas without the two ever coming into contact with each other. A typical shell and tube heat exchanger will contain a tube bundle inside an outer shell, or body. Cold water flows through these tubes, whilst hot water, or gas flows around the outside of the tubes, enabling the heat from the hot water or gas to be transferred to the colder water inside the tubes.

A good example of how the process works are swimming pools, where most are heated via a boiler, using Gas, LPG or Biomass as the energy source. In theory, the most efficient way to heat the pool would be to circulate the pool water directly through the boiler. But were this to happen, the chemicals used in the pool water to keep it safe for use, would quickly corrode and damage vital parts inside the boiler, leading to premature failure and a costly replacement.

However, by using a heat exchanger to act as an ‘interface’ between the boiler water circuit and the pool water circuit, the boiler is protected from damage and the pool water is quickly heated up to the required temperature; the pool water passing through the central ‘tube core’, whilst the hot boiler water circulates around the outside of the tubes, transferring heat energy to the pool water.

More examples of applications where Bowman heat exchangers are used.

In a shell and tube heat exchanger, coolant usually flows through the central ‘tube core’ to cool hot oil, water or air, which passes over and around the tubes. The direction in which the two fluids travel through the heat exchanger can be either ‘parallel flow’ or ‘counterflow’.

Parallel flow is where the fluid to be cooled, flows through the heat exchanger in the same direction as the cooling medium. Whilst this arrangement will provide cooling, it has limitations and can also create thermal stress within the heat exchanger, as one half of the unit will be appreciably warmer than the other.

In counterflow cooling, the incoming cooling medium absorbs more heat as the ‘hot’ fluid travels in the opposite direction. The cooling medium heats up as it travels through the heat exchanger, but as colder water enters the heat exchanger it absorbs more heat, reducing the temperature much lower than could be achieved with parallel flow.

The mean temperature difference between the cooling medium and the fluid being cooled is also more uniform along the length of the heat exchanger, reducing thermal stress.

Depending on flow rate and temperature, the heat transfer performance could be up to 15% more efficient with counterflow, possibly enabling a smaller heat exchanger to be used, saving space and money!

More information on the benefits of counterflow.

A CHP (Combined Heat and Power) unit generates electrical power and heat from a single energy source.

There are three primary components within a CHP unit, starting with the Prime Mover, (usually a reciprocating engine) that creates the motive power to drive the Electrical Generator. The final component is the Heat Recovery system, which comprises of single or multiple heat exchangers installed on key areas of the engine, to recover waste heat produced as a bye-product.

In an engine powered CHP unit, around 30% of the fuel used gets converted to electrical power. At the same time, around 50% of the fuel energy gets converted to heat. Without heat recovery, this valuable and highly usable energy stream would be lost to the atmosphere, wasting around half the cost of all fuel used to power the generator. By recovering this heat energy, the generating sets overall efficiency is improved to around 80% – even more in some installations – making CHP a highly efficient energy solution.

Recovered heat can be used for a wide range of domestic, commercial or industrial uses, including space heating and hot water, process heating, as well as cooling, or even generating more power!

Heat can be recovered from the engines exhaust stream, plus its cooling, lubrication and induction systems, using heat exchangers.

Bowman manufacture a comprehensive range of CHP heat recovery heat exchangers for exhaust gas, engine and induction cooling. For more information on Bowman CHP heat exchangers

Combined Heat and Power (CHP) is an extremely efficient method of generating electrical power and heat energy, from a single source.

Most ‘off-grid’ electricity is produced using an engine driven gen-set, usually powered by diesel or gas fuel.

However a typical gen-set, producing electricity only, is often only around 30% efficient.

That’s because only around 31% of the fuel used is converted to electrical power. The remaining 69% is lost throughout the operating cycle.

The largest element of energy loss is heat –  around 49% in total, so by recovering it, a valuable ‘free’ energy source is obtained, which also boosts the gen-sets overall efficiency to around 80%!

Heat exchangers are the most effective solution for recovering waste heat energy, as they convert it to hot water, which can be used for space heating, and hot water in residential or commercial buildings, industrial process heating, generating more power or even cooling via a chiller.

Heat can be recovered from virtually every area of the engine, including the exhaust stream, the cooling and lubrication systems, plus the induction air system.

Bowman manufacture a comprehensive range of CHP heat exchangers enabling customers to convert their gen-set into a highly efficient CHP system.