Cogeneration CHP, On Site Renewables, Renewables

Going the whole hog on CHP

biogas from Czech pig farm fuels cogen units


A large pig farm in the Czech Republic is currently operating its second CHP installation fuelled by biogas produced from farm slurry. Here, Vlado Murár and Radomír Řeháček describe the use of biogas in CHP plants and the installation at the pig farm, which is getting a return on investment by selling electricity to the grid.

Combined electricity and heat production is making headway into the use of renewable energy resources. Small cogeneration units increasingly use renewable fuels in what were traditionally fossil-fuel-fired applications. Waste treatment gas, landfill gas or biogas – examples of renewable fuels – are used by cogeneration plants based on combustion engines at sewage treatment works, municipal waste sites and agricultural sites. Many countries support the use of these alternative, renewable fuels in energy production by providing investment grants or advantageous purchase prices for renewable electricity. This is why the ‘green cogeneration’ market is beginning to show promising development.

Biomass – produced during anaerobic breakdown of biological material such as farm animals’ excrement or vegetable biomass – is especially attracting interest as it is a fully renewable energy source.


CHP units serve a pig farm at Velké Albrechtice in the Czech Republic. Biogas is considered a form of renewable energy in many countries

BIOGAS FOR ENERGY PRODUCTION

In terms of energy potential, biogas is similar to natural gas, the most commonly used fuel for cogeneration units. However, the sulphur content of biogas requires specific modifications to be made to the cogeneration equipment. Sulphur compounds can cause formation of acids (and thus corrosion) on inlet and flue gas tracts, oxidation/burning of spark-plug electrodes, and faster decomposition of lubrication oil. Modifications of CHP units therefore consist mainly of using more resistant materials for inlet and flue gas pipes, using more suitable materials (such as materials with minimum copper content) for the engine’s slide bearings, using lubrication oils with higher alkalinity, and adapting the frequencies of spark-plug and oil changes.

integrating district cooling and thermal energy storage with on-site power

District cooling is a well established technology in North America and is growing fast in certain other parts of the world – notably the Middle East. DC is often enhanced with thermal energy storage, which acts to smooth energy loads. Here, John Andrepont summarizes the benefits of these two technologies and some market trends.

District cooling (DC) applications are growing worldwide. The application of district cooling can often benefit the economics and performance of CHP and on-site power generation by providing a means of aggregating thermal loads. Its thermal loads can combine with and supplement seasonally variable heating loads to achieve a flatter demand profile for the thermal output of a CHP system. CHP systems are increasingly finding application within combined district heating and cooling systems.

District cooling is well established throughout North America. This includes many hundreds, if not thousands, of DC systems among single owner-user systems, such as university and college campuses, hospital/medical facilities, and other government and private commercial/industrial facilities. There are also many dozens of large (mostly urban) DC utility systems that have been developed increasingly over the past two decades. Growth continues to occur via the development of new systems as well as by the expansion of existing systems.

The application of district cooling can often benefit the economics and performance of CHP and on-site power 

Internationally, DC is growing in many other parts of the world, offering additional opportunities for CHP applications. The largest and fastest growing DC market is in the United Arab Emirates and the surrounding Gulf region. East and south-east Asian markets are also very significant. Many major new real-estate developments or re-developments there are utilizing DC. Also, parts of southern Europe and the developed economies of northern and western Europe – long-time users of district heating – are increasingly developing DC systems as well, as airconditioning becomes a more common requirement of building operation. Less mature DC markets, including Australia and South America, have increasing interest and activity underway.

Thermal energy storage (TES) is often integrated with DC systems, and is a common enhancement to DC systems at times of new construction and system expansions. TES not only enhances the operating economics of DC systems, it can reduce the necessary installed chiller plant capacity and thereby often reduces the net capital cost. TES also serves to level the 24-hour demand for cooling (and power), thus improving the economics for CHP or on-site power generation.