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Coal / Biomass / MSW

COAL

Coal is the traditional fuel of power plant. There is abundant storage of coal over the world, and developing cost is also quite low. With the characteristic of higher heating value and stable combustion, coal is the main fuel for power plant. Coal fired power plants, till now, are still the major electricity source for most of countries in the world, playing an important role in national economy and social production of each country.

According to the different coal ranks and other factors, coal can be divided into many types. The following data shall be evaluated for the coal used in thermal power plant, and these data have a significant impact on entire power plant system configuration and efficiency, etc.

  Anthracite Bituminous coal Lignite (Indonesia) Coal gangue
HHV(Kcal/kg) 5985 4605 3800 1512
LHV(Kcal/kg) 5768 4320 3401 1202
Car 64.95 48.51 38.7 14.8
Har 2.2 2.74 3.6 1.19
Oar 2.75 4.21 15.7 5.3
Nar 0.96 0.84 0.8 0.29
Sar 0.29 0.32 0.2 1.5
Aar 20.65 32.78 5 67.1
Mar 8.2 10.6 36 9.82
Vr 8.48 26.47 40 45.03

※ The data above are approximate value for reference only.

Different coal should adopt different furnace combustion method, so as to acquire stable and sufficient combustion, improve efficiency of boiler, whole power plant, and suppress & reduce poisonous gas emission (such as SOx, NOx etc.). Normally, boiler can be divided into following types: stoker boiler (Clockwise, counter-clockwise, spreader stoker, reciprocating grate, etc.), bubbling bed boiler, CFB boiler, pulverized coal boiler etc., among which, CFB boiler, gifted by the feature of wide adaptability of different coal, sufficient combustion, and environment friendly (achieve the desulfurization inside furnace and reduce the emission of NOx with low temperature combustion), is widely adopted in the small & medium sized power plants in recent years, which has brought great economic and social benefits.

BIOMASS

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Biomass energy is a kind of typical renewable energy, and actually is the solar energy which is fixed on the earth through plant photosynthesis. It is estimated that the annual energy stored by the green plants is equivalent to 10 times of main fuel consumption in the world. However, the utilization of biomass energy is still less than 1% of its total energy. Biomass is most likely to become one of the major new energy in 21st century. Making use of biomass energy instead of fuels such as oil, coal and natural gas can reduce our dependence on fossil energy and protect the nation's energy resources. Therefore, countries around the world encourage the development of the biomass projects.

Our company has strategically collaboration with Shandong Provincial Key Laboratory of Biomass. For every biomass power plant that clients plan to build, we will take a fuel test on the biomass fuel to collect the physical and chemical index including main components, fuel value and combustion characteristics. Therefore, we can choose the most suitable boiler and take optimized design for boiler purposely, which ensures the whole plant running smoothly, reliably and efficiently.

According to the different characteristics of fuel, the biomass power plant can be divided into the following categories:

I. Wood-fired power plant

The wood processing factories requires a lot of electricity and steam. Meanwhile, they also produce a lot of wood waste and offcuts. So for the wood processing factories, it has high economic benefits to build a wood-fired captive power plant. For wood-fired power plant, the fuel handling system and boiler are the keys to the project. In wood-fired power plant design, especially feeding system, our company has developed mature proposal on the wood-fired power plant design, especially on the fuel handling system. In addition, the technology of wood-fired boiler in China is really quite mature. Turbine & generator units are normally with extraction type and back pressure type.

II. Bagasse-fired power plant

The bagasse-fired power plants are widely used in sugar factories. There are a lot of sugar factories in Guangxi Province of China, Indonesia, Malaysia and other places. The bagasse as a fuel, which is produced in the sugar refining process, is combusted in the tailor-made boiler to produce the steam and drive a turbine generator to generate electricity. The steam and electricity are used to meet the demand of sugar refining process.

III. Palm waste fired power plant

Palm oil mill requires a lot of steam. The milling process also produces waste such as empty fruit bunches, palm fruit fibers, palm shell, palm kernel, etc. As a kind of fuel, palm wastes are combusted in the tailor-made biomass boiler to generate steam. The steam drives the back pressure type steam turbine to produce electricity and then goes to boil the palm fruit directly. It not only meets the requirements of electricity and steam, but also solves the problems of palm waste disposal.

IV. Rice husk-fired power plant

Compared with other biomass fuels such like waste wood, bagasse, etc., rice husk is a little difficult to burn. The carbon of rice husk is not easy to be combusted completely. Then according to the characteristics of rice husk, we have taken the structure & secondary air into consideration during design stage. With sound arrangement of furnace combustion, the carbon content in the ash can be controlled. Along with power generation, rice husk ash can be used to produce active carbon, white carbon black, high purity SiO2, and other by products.

V. Straw-fired power plant

Straw is the stems and leaves left after crop has been picked and threshed. There are mainly straws of corn, wheat, rice, sorghum, soybeans and so on. Straw-fired power plant is the important strategic move to develop the recycling economy vigorously and transform economic growth mode by making use of renewable resources. At present, straw power generation is growing rapidly. Straw is a kind of very good clean & renewable energy. The calorific value of every two tons of straw is equivalent to one ton of standard coal, and the average sulfur content of straw is only 3.8 ‰. While for coal, the average sulfur content of coal amounts to about 1%. In the process of biomass recycling, CO2 emission is balanced with CO2 absorption during biomass recycling, which has realized the CO2 zero emission result.

MSW

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Garbage power generation refers to burn the municipal solid waste by special combustion boiler, and then generate electricity by steam turbo-generator set. MSW power generation firstly need to collect all kinds of garbage, and then sort them to process. The garbage with high heat value can be burned with high temperature, and the heat energy produced during high temperature combustion is converted into high temperature steam. The steam drives steam turbine to rotate the generator for electricity. For the organics unfavorable to combustion, we can take fermentation, anaerobic treatment, and finally dry it together with desulphurization. A kind of gas named methane is produced, also called marsh gas. Then through combustion, thermal energy is converted into steam, which propel turbine to rotate and drive generator to generate electrical energy.

MSW power generation technology gradually has become mature. There are mainly two types of Garbage Combustion Boilers, one is the mechanical grate type and another is fluidized bed type of boiler.

Mechanical Grate type and Fluidized Bed type boiler are main combustion equipments of large scale MSW combustion boiler. Mechanical Grate Combustion Technology is more suitable for High Heat Value MSW, and the Low Heat Value and high moisture MSW need to be added fuel oil to assist combustion. Fluidized Bed Technology has excellent adaptability for Low Heat Value MSW, higher combusting efficiency, which could enable MSW get sufficient heating, drying and comparatively complete combustion. However, this kind of technology should pay more attention to reduce secondary pollution.