Variants of Plants and Practices for Cogeneration

A Stirling engine or a reciprocating engine may be used in smaller cogeneration units.
The radiator and exhaust are used to remove heat. Because small gas and diesel engines are less expensive than small gas or oil-fired steam-electric plants, the systems are popular in modest capacities. Some cogeneration facilities use biomass, as well as commercial and municipal solid waste, as fuel. Some CHP plants generate heat and electricity using waste gas as the fuel. Waste gases include sewage gas, landfill gas, gas from coal mines, gas from animal waste, and gas from flammable industrial waste. For added technical and environmental performance, some cogeneration plants combine gas and solar photovoltaic generation. These hybrid systems can be scaled down to the level of a building or even a single residence.
Five main technologies are used in micro CHP installations: microturbines, IC engines, Stirling engines, closed-cycle steam engines, and fuel cells. The most affordable of the so-called microgeneration technologies for reducing carbon emissions, according to one author’s 2008 analysis, is MicroCHP based on Stirling engines. When using natural gas, it depends on steam reforming to transform natural gas into hydrogen before it is used in the fuel cell. As a result, this continues to emit CO2 (see reaction), although running on this can be a reasonable solution (temporarily) while waiting for the hydrogen to start being dispersed through the (natural gas) piping system. An electricity-producing condensing furnace that runs on natural gas or propane is another example of a Micro CHP system. It combines the cogeneration fuel-saving method, which creates useable heat and electricity from a single combustion source. The condensing furnace is a forced-air gas system with a secondary heat exchanger that enables heat to be recovered from water vapor as well as heat to be collected from combustion products down to the ambient temperature. A water drain and vent to the side of the building are used in place of the chimney.
In pulp and paper mills, refineries, and chemical factories, cogeneration is still prevalent. The heat is often recovered in this “industrial cogeneration/CHP” at higher temperatures (over 100 deg C) and used for process steam or drying tasks. Compared to low-grade waste heat, this is more valuable and adaptable, although there is a minor loss in power generation.
Smaller industrial co-generation units are a viable off-grid solution for a range of remote applications to cut carbon emissions. These units have an output capacity of 5 MW to 25 MW. Compared to utilities, industrial cogeneration units typically operate at much lower boiler pressures. One of the causes is that returning condensate to cogeneration units may be contaminated. Industries typically need to treat proportionately more boiler makeup water since boiler-feed water from cogeneration units has significantly lower return rates than 100% condensing power plants. The feed water for boilers must be totally de-mineralized and oxygen-free, and the higher the pressure, the more important it is that the feed water be as pure as possible.
The use of sugarcane bagasse for energy production has advantages for the environment over the use of fossil fuel-based thermoelectric plants, such as natural gas, because it emits less CO2. Along with the benefits to the environment, cogeneration utilizing sugarcane bagasse offers advantages in terms of efficiency when compared to thermoelectric generation, thanks to the use of the generated energy. While some of the heat generated during thermoelectric generation is lost, with cogeneration, this heat may be utilized in the manufacturing processes, improving the process’ overall efficiency.