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The generation of electricity and heat with no pollution and with considerably less emission of the greenhouse gas CO2 sounds too good to be true. However, it is possible with the so-called SOFC fuel cells, which Risø has been conducting research into for over 20 years. The technology is now on its way to reach Danish and international companies including consumers.

An SOFC fuel cell produces electricity and heat with a very high efficiency. That means less carbon emissions for each kW produced. Furthermore, the production of electricity happens with nearly no emissions of pollutants such as nitrogen and sulphur oxides. Thus, SOFC fuel cells are a strong card in the future climate-friendly energy supply. SOFC fuel cells are flat and thin as a piece of paper, providing a voltage of approx. 1 volt. They are put together in stacks to achieve the desired voltage and wattage.

Dantherm Power’s micro CHP plant will in its final shape in 2015 be the size of a dishwasher. (Credit: Image courtesy of Risoe National Laboratory for Sustainable Energy, the Technical University of Denmark)

Each home will have a micro CHP plant of its own

To accommodate more renewable energy, the future electricity system will look significantly different from now. E.g. it is believed that today’s large, central CHP plants will be supplemented with numerous quite small CHP plants of a few kW, in each home. These micro CHP plants in homes can help balance energy in the future energy system, where more energy will be coming from renewable energy sources such as the wind and the sun. The micro CHP plants will be taking over energy production, for example, when there is no wind, and when the sun is hiding behind a cloud.

“Topsoe Fuel Cell provides the engine, we produce the rest of what is to surround the engine in order to finally end up having a fully operational micro CHP plant,” says Jesper Themsen from Dantherm Power. The core technology at Topsoe Fuel Cell is based on fuel cells developed at Risø DTU.

“At the moment, we are developing compact micro CHP plants, similar to a conventional oil or gas furnace when it comes to generating heat for the home. What’s new about micro CHP plants, is that they also produce the power the home needs. In this way, you avoid transmission loss in the electricity and district heating network,” says Jesper Themsen, technical director at Dantherm Power. Simultaneously, the micro CHP plants emit no or very little pollution and less carbon.

“In the spring of 2010 we produced a few micro CHP plants as part of the project ‘Danish micro cogeneration’. Now we’re doing tomorrow’s micro CHP plant in cooperation with Topsoe Fuel Cell, and in October 2010, we produced two systems that we will put into operation among professional users, for example plumbers or electricians. People with craftsman experience who can help us solve the problems that naturally arise with the plants during the first phase, “says Jesper Themsen. The first plants will generate 1 kW of power and 1 kW of heat and will be powered by natural gas.

“Subsequently, we will produce five micro CHP plants, which will also be put into operation among professional users. We are still in the early process of the technological launch and need to gather as much experience with these systems as possible,” says Jesper Themsen.

The micro CHP plants are based on Topsoe PowerCores™. Dantherm Power will build the rest around them. It should be possible to add natural gas purified of sulphur and with the correct pressure. There must be supply of fresh air, a heat exchanger and a heat store. The necessary electronic control for the micro CHP plant to be connected to the grid will be incorporated. Last but not least, the micro CHP plants will have to gain security clearance.

Currently, micro CHP plants are the size of an overgrown American fridge. “It’s not that we cannot make them smaller, but here to start with it should not be too compact, but easy for one to supervise and maintain the various parts of the plant,” says Jesper Themsen.

Dantherm Power expects to have seven micro CHP plants in operation in early 2011, which will be in operation throughout the entire heating season and well into spring 2011.

In September 2011, Dantherm Power plans to produce 15 new micro CHP plants based on experiences from the first seven. “They’ll be so reliable that we can install them in private homes in Southern Jutland,” says Jesper Themsen and continues: “In 2012, we believe that SOFC micro CHP plants will be affordable and have the desired properties, allowing ordinary people to easily replace their old furnace with a SOFC micro CHP plant.”

Jesper Themsen expects a major breakthrough to happen in 2013 — 2015 and that many Danish families in 2015 will be having a SOFC micro CHP plant, which will not take up more space than a dishwasher. Fuels will initially be natural gas, later it could be methanol and liquefied petroleum gas. In the long term, biofuels could also prove useful.

“We are having a long-term strategic cooperation with Topsoe Fuel Cell on SOFC micro CHP plants, and we are working mutually to make SOFC fuel cell power plants a commercial success,” says Jesper Themsen.

In the long term, he imagines that fuel cell power plants will replace generators powered by diesel or gas. They are used as backup in countries where the grid is not as stable as in Denmark. Here they are in operation continuously for many hours with the purpose of using the fuel efficiently.

Risoe National Laboratory for Sustainable Energy, the Technical University of Denmark (2010, November 29). ‘Green’ way to generate heat and electricity with use of fuel cells. ScienceDaily. Retrieved November 29, 2010, from http://www.sciencedaily.com­ /releases/2010/11/101129111733.htm

There are lots of issues to be considered about fuel cells, and those that are heavily into fuel cells are likely to want to know more. Even if this article serves as no more than an introduction to fuel cells, nothing stops you from putting the information to good use.

The Original Post is Located Here: ‘Green’ Way to Generate Heat and Electricity With Use of Fuel Cells

Biomass Gasification

There are many ways to generate electricity from biomass using thermo-chemical pathway. These include directly-fired or conventional steam approach, co-firing, pyrolysis and gasification.

1. Direct Fired or Conventional Steam Boiler
Most of the woody biomass-to-energy plants use direct-fired system or conventional steam boiler, whereby biomass feedstock is directly burned to produce steam leading to generation of electricity. In a direct-fired system, biomass is fed from the bottom of the boiler and air is supplied at the base. Hot combustion gases are passed through a heat exchanger in which water is boiled to create steam.

Biomass is dried, sized into smaller pieces and then pelletized or briquetted before firing. Pelletization is a process of reducing the bulk volume of biomass feedstock by mechanical means to improve handling and combustion characteristics of biomass. Wood pellets are normally produced from dry industrial wood waste, as e.g. shavings, sawdust and sander dust. Pelletization results in:

1. Concentration of energy in the biomass feedstock.
2. Easy handling, reduced transportation cost and hassle-free storage.
3. Low-moisture fuel with good burning characteristics.
4. Well-defined, good quality fuel for commercial and domestic use.

The processed biomass is added to a furnace or a boiler to generate heat which is then run through a turbine which drives an electrical generator. The heat generated by the exothermic process of combustion to power the generator can also be used to regulate temperature of the plant and other buildings, making the whole process much more efficient. Cogeneration of heat and electricity provides an economical option, particularly at sawmills or other sites where a source of biomass waste is already available. For example, wood waste is used to produce both electricity and steam at paper mills.

2. Co-firing
Co-firing is the simplest way to use biomass with energy systems based on fossil fuels. Small portions (upto 15%) of woody and herbaceous biomass such as poplar, willow and switch grass can be used as fuel in an existing coal power plant. Like coal, biomass is placed into the boilers and burned in such systems. The only cost associated with upgrading the system is incurred in buying a boiler capable of burning both the fuels, which is a more cost-effective than building a new plant.

The environmental benefits of adding biomass to coal includes decrease in nitrogen and sulphur oxides which are responsible for causing smog, acid rain and ozone pollution. In addition, relatively lower amount of carbon dioxide is released into the atmospheres. Co-firing provides a good platform for transition to more viable and sustainable renewable energy practices.

3. Pyrolysis
Pyrolysis offers a flexible and attractive way of converting solid biomass into an easily stored and transportable fuel, which can be successfully used for the production of heat, power and chemicals. In pyrolysis, biomass is subjected to high temperatures in the absence of oxygen resulting in the production of pyrolysis oil (or bio-oil), char or syngas which can then be used to generate electricity. The process transforms the biomass into high quality fuel without creating ash or energy directly.

Wood residues, forest residues and bagasse are important short term feed materials for pyrolysis being aplenty, low-cost and good energy source. Straw and agro residues are important in the longer term; however straw has high ash content which might cause problems in pyrolysis. Sewage sludge is a significant resource that requires new disposal methods and can be pyrolysed to give liquids.

Pyrolysis oil can offer major advantages over solid biomass and gasification due to the ease of handling, storage and combustion in an existing power station when special start-up procedures are not necessary.

4. Biomass gasification
Gasification processes convert biomass into combustible gases that ideally contain all the energy originally present in the biomass. In practice, conversion efficiencies ranging from 60% to 90% are achieved. Gasification processes can be either direct (using air or oxygen to generate heat through exothermic reactions) or indirect (transferring heat to the reactor from the outside). The gas can be burned to produce industrial or residential heat, to run engines for mechanical or electrical power, or to make synthetic fuels.

Biomass gasifiers are of two kinds – updraft and downdraft. In an updraft unit, biomass is fed in the top of the reactor and air is injected into the bottom of the fuel bed. The efficiency of updraft gasifiers ranges from 80 to 90 per cent on account of efficient counter-current heat exchange between the rising gases and descending solids. However, the tars produced by updraft gasifiers imply that the gas must be cooled before it can be used in internal combustion engines. Thus, in practical operation, updraft units are used for direct heat applications while downdraft ones are employed for operating internal combustion engines.

Large scale applications of gasifiers include comprehensive versions of the small scale updraft and downdraft technologies, and fluidized bed technologies. The superior heat and mass transfer of fluidized beds leads to relatively uniform temperatures throughout the bed, better fuel moisture utilization, and faster rate of reaction, resulting in higher throughput capabilities.

Written by Salman Zafar

Email: salman.alg@gmail.com

The Original Post is Located Here: Woody Biomass Conversion Technologies