Types of Cogeneration Technology
Cogeneration, or CHP (‘Combined Heat & Power’), is the process of generating both heat and electricity in usable forms through an environmentally-friendly production process. This process requires the use of a CHP process, which utilises fuel such as gas, biogas or diesel in order to produce power. We won’t go into details here as to how the CHP cogeneration system works, however the process will always require an electricity generator, otherwise known as an engine, and a heat recovery system. There are two major types of CHP cogeneration engines, and we will give you a bit of information about both of them below.
CHP Cogeneration Engines
The two major types of generators used in CHP systems are combustion engines and turbine engines. Each have their respective benefits and downfalls, but both offer a practical option when it comes to the cogeneration process.
What is an engine?
In essence, an engine is any piece of equipment that converts varying forms of energy into motion or force.
The combustion engine is one of the most well-known types of engines around, as it is normally used in cars and commercial vehicles. It can however be used for cogeneration, and is quite frequently used for smaller CHP plants. They are in a very similar form to car or truck engine, and work in a very similar way.
The principle behind any internal combustion engine is that if you put a small amount of high-energy-density fuel in a tiny enclosed space and ignite it, a large amount of energy is released in the form of expanding gas.
The process used by a combustion engine can get a little complicated, however we will address the basics and see how we go. Combustion, also known as burning, is a basic chemical process whereby energy is released from an air and fuel mix. In an internal combustion engine, both the ignition and combustion of fuel happens in the actual engine itself. The engine then partially converts the energy from the combustion to run.
The engine runs as follows :
- The connecting rod connects the piston to the crankshaft. As the crankshaft goes around, it is like you are ‘resetting a cannon’. The piston begins at the top and the intake valve opens
- The piston moves down to let the engine take in a cylinder full of air and fuel, which is known as the intake stroke. A really small amount of fuel (the tiniest drop!) is needed to be mixed with the air for this process to work
- The cylinder then moves back up to compress the air and fuel mixture. The reason for this is compression makes for a more powerful explosion
- When the piston gets back to the top, otherwise known as the ‘top of its stroke’, the spark plug will let out a spark to light up the fuel. The fuel in the cylinder will then explode, which drives the piston down
- Once the piston hits the bottom, otherwise known as the ‘bottom of its stroke’, the exhaust valve will open and the exhaust leaves the cylinder.
The engine will then be ready to start it all again, and will commence the next cycle with another intake of air and gas.
*Did you know? Most combustion engines are 4-stroke, meaning four piston strokes are needed to complete a cycle. The cycle includes four processes: intake, compression, combustion and power stroke, and exhaust.
An altered car combustion engine combined with inverter technology is the type of generator that Inoplex uses for their CHP process!
The other type of engine used in CHP plants is a turbine engine. They are generally used in larger CHP plants, which use either gas or steam turbine engines as opposed to combustion engines in the cogeneration process.
All turbine engines use the same principle to work – that is, production of thrust to propel something forward. They take in air, that air is burnt with fuel and the hot exhaust gas comes out, forming thrust. This is otherwise known as the principle of Newton’s Third Law of Motion to provide propulsion force (thrust).
In theory, turbine engines are quite simple. They have 3 parts – a compressor, a combustion area and a turbine – which work together to create thrust. The parts work together as follows:
- Air is drawn in from the right of the compressor. The compressor looks like a cone-shaped cylinder which has rows of small fan blades attached to it (the amount of blades depends on the engine)
- The air is then forced through the compressor, where pressure significantly increases
- The high-pressure air then gets to the combustion area, where fuel injectors will insert a constant flow of fuel. The flame holder, otherwise known as the ‘can’, is a hollow, perforated piece of heavy metal which keeps a flame burning consistently (which is quite tricky when you think about it, due to the high pressure air moving around super quickly in the combustion area)
- To the left of the engine is the turbine section, which usually contains the turbines, the shaft and the compressor. One set of turbines drives the compressor and the turbines, the shaft and the compressor all turn as one
- The final turbine stage drives the output shaft, which has a single set of vanes. The final turbine stage and the output shaft are their own entity, they stand alone and are a freewheeling unit. They run and spin without needing to be connected to any other part of the engine and the hot gases that blow through the final turbine stage generate heaps of energy.
What makes a combustion engine and turbine engine different?
Although turbine engines and combustion engines run off similar scientific principles, the major difference is the power the engines can produce. A turbine engine is a lot more powerful than a combustion engine, because :
- Turbine engines can burn more fuel (based on the physics principle of the Law of Conservation of Energy, which says that if an engine needs to make more power each second, it has to burn more fuel each second)
- Because intake, compression, combustion, and exhaust all happen at the same time, a turbine engine produces maximal power all the time (unlike, for example, a single cylinder in a piston engine)
- Unlike a combustion engine, a typical turbine engine passes its exhaust through multiple turbine ‘stages’ to get as much energy out of it as possible. This makes it much more efficient, meaning it gets more power from the same amount of fuel
This is why turbine engines, not combustion engines, are generally used to power jets and other aircraft and they are used to power larger CHP plants (as opposed to combustion engines, which power smaller CHP systems and vehicles such as cars or trucks).
What fuel can a CHP cogeneration engine run off?
An engine used in the cogeneration process can use a range of fuels, including diesel, biogas, natural gas and LPG.
Where does the heat from the CHP engine come from?
One of the major benefits of the cogeneration process is the fact that both electricity and heat are final products. When it comes to heat, the following key areas produce the most heat to be recovered :
- Engine exhaust gases
- Cooling water for the engine jacket
- First stage air intake intercooler
- Cooling of the engine lubrication oil
- Engine generator radiated heat (second stage intercooler)
Your cogeneration technology experts
If you would like to know more about the cogeneration process, CHP engines and how they can benefit you, give Inoplex a call on 1300 113 782 or complete an online enquiry formtoday. We are specialists in cogeneration technology and will be able to advise as to the best option for you and your business.