1Research status of biomass briquette fuel technology
1.1 Energy shortage and over-reliance on fossil fuels have caused serious
environmental pollution
With the rapid development of the economy, the consumption of fossil energy
is increasing year by year. In 2001, my country's CO2 emissions reached 3
billion tons, accounting for 13% of global emissions and ranking second in the
world. my country's environmental pollution problem is becoming increasingly
serious.
1.2 Biomass resources are abundant, but the current utilization rate is
very low and the waste is serious.
The total amount of biomass organic matter resources in my country (straw,
forest residues, etc.) reaches more than 900 million tons [1]. Biomass energy is
clean, renewable, contains very little S, has zero CO2 emissions, and is widely
distributed. Due to the low stability and reliability of biomass briquette fuel
equipment, the processing cost is high. At present, the utilization rate of
biomass is still very low, and the phenomenon of burning is repeated and the
waste is serious.
1.3 Research status of foreign biomass briquette fuel technology
The main use of straw in the United States is baling technology, and its
use is not as fuel, but as feed or raw materials for other industries. European
countries mainly use biomass as fuel and power generation, replacing oil and
coal. Processing equipment, boilers, hot blast furnaces, power generation
equipment, etc. have all been industrialized and scaled. The combustion
equipment of biomass briquette fuel in Japan, the United States and some
European countries has been finalized and industrialized, and has been widely
used in heating, heating, drying, power generation and other fields [2].
At present, there are four foreign biomass molding methods, namely ring die
and flat mode, screw extrusion, mechanical piston and hydraulic piston. Spiral
extrusion was the earliest developed and has always occupied a dominant position
in Southeast Asian countries such as India, Thailand, and Malaysia and my
country.
1.4 Current Research Status of Domestic Biomass Molded Fuel Technology
China introduced spiral biomass forming machines in the 1980s. After 1990,
Shaanxi Wugong, Henan Gongyi, Hunan Rural Energy Office and other units have
developed and produced several different specifications of biomass forming
machines and carbonization units. In the 1990s, Henan Agricultural University
and China Agricultural Machinery and Energy Power Research Institute
respectively developed PB-I mechanical stamping type, HPB series hydraulically
driven and CYJ mechanical stamping forming machines. Since the 21st century, the
development of biomass pellet molding technology has become increasingly mature.
Dozens of domestic companies such as Jiangsu Zhengchang Company, Jilin Huaguang
Institute, Henan Academy of Sciences Institute of Energy, and Henan Derun have
successively developed various types of ring-die and flat-die pellet forming
machines based on pellet feed machines. At the same time, supporting
biomass-specific boilers and domestic furnaces were developed.
2 Key technologies of biomass briquette fuel
2.1 Raw material collection is the technical bottleneck that restricts the
development of briquette fuel technology (collection, transportation,
storage)
The collection of biomass raw materials in China is different from that in
foreign countries. The management systems are different, the plots are small and
scattered, the level of collection mechanization is low, and there is no
schedule for bundling and directional collection, making collection difficult.
Without sufficient raw materials, biomass briquette fuel technology cannot
develop rapidly. The collection of raw materials is a technical bottleneck
restricting the development of pellet fuel technology.
2.2 Diversity and complexity of biomass raw materials themselves
There are many types of biomass raw materials, and their contents of
lignin, cellulose, pectin and other ingredients vary greatly. Biomass raw
materials have poor force conductivity and strong resilience, and the conditions
under which they are compressed and molded are also very different. Biomass raw
materials are compressed from low density to high density raw material feeding
problems. The moisture content of the raw materials changes with the type of raw
materials, region, season and climate. Therefore, the moisture content of the
raw materials has become a major problem restricting hot press molding.
2.3 The harsh working environment of molded fuel equipment
The large amount of dust, soil and sand carried by the biomass raw
materials during the collection process will not only increase the wear of the
molding parts, but also cause pollution to the lubrication system of the molding
equipment, affecting the service life and stable operation of the equipment.
Therefore, improving the service life of molded parts is another problem in
molding technology.
2.4 Slagging and contamination tendency during the combustion process of
molded fuel
Biomass raw materials contain a lot of potassium, calcium, iron, silicon,
aluminum and other components, which are easy to burn and ash at high
temperatures, and are easy to form slagging and deposition on the heat transfer
wall, which directly affects the conduction of heat and the heat of the stove.
Utilization.
2.5 Tar precipitation problem under low temperature conditions during the
combustion process of molded fuel
Intermittent combustion is the main feature of energy consumption in rural
areas. The fire sealing performance of biomass stoves is better, and because the
temperature in the furnace decreases after the fire is sealed, a large amount of
tar will precipitate from the straw with high volatile content, which will cause
the chimney and furnace to collapse in a short period of time. Clogged mouth and
other parts.
3 Biomass molding fuel molding process and equipment
3.1 Biomass straw molding fuel recycling technology
(1) Process flow
Collection of biomass raw materials→drying→pulverization→forming→combustion
(as shown in Figure 1).
(2) Process equipment
The equipment used in the process includes collection equipment, drying
equipment, crushing equipment, forming equipment, biomass-specific combustion
furnaces, various domestic furnaces and burners. Among them, the molding machine
is the key equipment. According to the different molding methods, the biomass
molding machine can be divided into spiral extrusion molding, molding (flat die
and ring die) molding, piston stamping (mechanical and hydraulic) molding and
briquetting molding.
3.2HPB series biomass straw hydraulic forming machine
Henan Agricultural University began to develop hydraulic piston HPB series
molding machines and special combustion furnaces in 1998; in 2000, it received
financial support from the Ministry of Science and Technology; in 2001, it
transferred technology to enterprises; in 2003, the Henan Provincial Department
of Finance conducted a pilot demonstration; in 2004 After the year, it was
promoted and applied in Beijing, Xinjiang, Jilin, Liaoning, Jiangsu, Shandong,
Zhengzhou Agricultural High-tech Park and other places in China, and the molded
fuel was tested in small boilers, greenhouse plastic greenhouse heating, and
farmers' domestic stoves. Research [3-4]. Test results prove that straw
briquette fuel is a renewable high-quality fuel with better combustion
characteristics than ordinary coal, lower price than coal, and less pollution in
combustion exhaust gas than coal. The 7 Central Science and Technology Gardens,
the Daily Agricultural Economics column and some domestic newspapers and
periodicals have carried out special reports. At present, the technology has
been transferred to 4 companies, and a total of 5 generations of HPB series
biomass straw hydraulic forming machines have been developed. The market of the
5th generation products is running well.
3.3 Characteristics and uses of biomass briquette fuel
Rich raw materials, agricultural and forestry wastes, various crop straws,
etc.; high cellulose content, about 70%; S content is much lower than coal; high
fuel density, 0.8 to 1.3, easy to store and transport; product shapes and
specifications are many, including pellets and rods , lumps, etc., with a wide
range of utilization; the calorific value is equivalent to that of
medium-quality coal, the burning speed is more than 11% faster than coal, the
combustion is complete, the black smoke is low, the ash content is low, it is
environmentally friendly and hygienic, and can be used with high grade; it can
form industrial, economic and The social and environmental benefits are
obvious.
It can replace coal as a fuel for biomass-specific burners, boilers,
fireplaces, tea stoves, power generation stoves and rural domestic stoves. It
can effectively solve the problem of straw burning in rural areas, alleviate the
energy shortage problem in some areas, and protect the atmospheric environment.
It has good Industry prospects.
4. Development Prospects of Biomass Molded Fuel Technology
(1) The equipment required for biomass straw collection from the field →
drying → crushing → forming → burning must be matched in order to be promoted
and applied in rural and urban areas [5]. The collection link is the bottleneck,
and biomass straw collection equipment must be developed.
(2) Biomass straw resources are large and sufficient, covering a wide area,
low in price, and can be recycled. Agronomic experts have proposed that an
appropriate amount of straw should be returned to the fields, and that all straw
cannot be returned to the fields year after year. The amount of feed treatment
is limited. Most areas have adopted measures to ban straw burning, which
provides raw material guarantee for the development of briquette fuel
technology.
(3) Coal-burning pollution in my country's cities is serious. Large and
medium-sized cities have banned coal-fired boilers below 2 tons. They are eager
to find clean alternative energy and switch to natural gas or electricity. The
cost is higher. However, the shortage of natural gas and oil and their heavy
reliance on imports have affected National energy security [6-7]. This brings
opportunities for the development of biomass briquette fuel technology.
(4) It is predicted that the underground reserves of oil, natural gas and
coal will only be enough for about 60 years at the current utilization rate.
According to FAO's latest report in 2000, biomass power generation and
high-grade energy utilization will account for 40% by around 2050. It can be
seen that using biomass as fuel after forming is the future development
direction of international renewable energy.
(5) The country has formulated medium- and long-term development goals for
biomass energy: the utilization of biomass briquette fuel will increase from the
current less than 500,000 tons/year to 20 million tons/year by 2020. This has
found a market for the application of biomass briquette fuel technology.
(6) The country has promulgated many laws and regulations related to the
utilization of biomass energy, and some regions have included biomass pellet
fuel equipment in the catalog of agricultural machinery subsidies. The
"Renewable Energy Law" was officially implemented on January 1, 2006. In 2009,
the Ministry of Agriculture will promulgate and implement standards for the
technical conditions and test methods of biomass briquette fuel and briquette
equipment. The processing and production of biomass molding equipment and
molding fuel will be more standardized.
(7) The dust and emission indicators after combustion of biomass briquette
fuel are lower than those of coal, which can reduce CO2 and SO2 emissions,
reduce the greenhouse effect, and effectively protect the ecological
environment. After biomass pellet fuel enters large-scale production, it not
only has obvious environmental protection benefits, but also provides employment
for farmers, increases income, and has significant economic and social
benefits.
(8) From the analysis of the molding equipment, the molded fuel equipment
is simple to operate, easy to use, and suitable for rural use. The processing
technology of the crusher and forming machine is not complicated. The service
life of the consumable parts of the hydraulic forming machine has reached more
than 1000 hours. The energy consumption per unit of crushing and forming
products can be reduced to 60kWh/t. The production of biomass pellet fuel is
placed in rural areas, and the use of pellet fuel furnaces can be located in
medium and small towns or rural areas, so that the straw crushing, molding and
burning can be industrialized.
(9) Biomass-specific combustion furnaces and boilers are basically mature.
The designed small biomass burning furnace (domestic and heating) has been used
in rural areas, with good combustion effect and fire sealing time of 12 to 24
hours.
(10) Through pilot demonstrations in previous years, some experience in
large-scale production of biomass briquette fuel has been obtained, and a
variety of large-scale production demonstration models and management models
have been explored. The stability, reliability and main performance indicators
of biomass briquette fuel equipment have been greatly improved.
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