Status and Prospects Analysis of coal briquette Technology

wuqi Wen*; shiqi Jin; shiping Jin; shunli Fang; xilai Zhang; suyi Huang; liangsuo Shu; yongxiang Zhang,

Huazhong University of Science and Technology, Wuhan, China

*email: wenwuqi1984@163.com

Keywords: coal briquette; molding; additives; biomass briquette

Abstract: This paper analyzes the current energy structure and coal we use, based on clean coal

technology in China, one of the current technology development status and prospects of coal were

analyzed, and highlights China's Hunan province a coal for flue-cured tobacco production - biomass

briquette mix, production test proved its superior performance, the desulfurization rate, burn rate of

more than 90%, respectively, and 98%, suitable for promotion.

Introduction

China is the world superpower of coal production and consumption, and now the annual output has

reached more than 1.4 billion tons. Currently, China's coal provides about 70% of primary energy,

and this coal-based structure will remain a longer period, which is our conditions determined by the

energy structure, and was particularly prominent in China, as shown in Table 1 [1].Coal as an energy

source has made great contributions for human development, but during the coal development and

utilization process, there also produced a series of pollution problems, which threatening the

ecological balance and human survival.

Table 1 China fossil fuel reserves and mine life Recoverable

energy type Proved reserves Standard coal equivalent Mineable life (years)

coal 1145 billion t 817 billion t 102

oil 32.6 billion tons 47 billion t 23

Uranium 5.1 billion tons 30

natural gas 11270 billion m3 15 billion t 61

According to statistics, industrial experimental results show that coal briquette-fired industrial

boiler thermal efficiency can be increased by 10% to 17%, coal consumption rate is 10% to 26%,

civilian coal briquette stove coal consumption rate is 20%. Dust emissions can be reduced 71% to

89%, 3,4-benzopyrene reduced 50% to 60%, NOx reduced 50% to 60%. So, development coal

briquette technology has very significant economic efficiency and environmental effect

[2].

Coal briquette technology

Coal briquette can be divided into industrial and commercial coal briquettes. Raw coal is the main

material, adding the specific use ratio of binder, oxidizer and desulfurization agent, and then

mechanical pressed into a certain strength and size and shapes of the coal products [3]. Compared

with coal-burning, it can typically improve 15% to 20% of consumption coal rate and 10% to 15%

of thermal efficiency, reducing 60% to 80% of soot emissions, a strong carcinogen (Bap) by 50% or

more. If add sulfur agent coal, SO2 and NOx emissions also can be reduced 50% to 60% [4]. So coal

briquette technology not only can improve their economic value of low-quality coal pulverized coal,

peat, lignite, but also can give people the use of a relatively clean environment in the process.

Applied Mechanics and Materials Vols. 178-181 (2012) pp 98-101Online available since 2012/May/14 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.178-181.98

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Today, China has become the world's production and use of coal-fired industrial boilers than

any other country. The coal consumption of coal-fired boilers is about one-third of the country's

total coal output each year [5][6]

. Thus the use of coal technology research and extension is extremely

important in the industry. The following will focus on development status of China's coal

technology.

Fig.1 Coal briquette workflow

Industrial coal briquette technology

The main forming technical of China's coal industry are the briquette molding technology, the use

of additives, as well as the rapid development biomass briquette technology in recent years, the

workflow is shown in Fig.1.

1) molding process

The main coal forming process has binder and binder-free molding. Binder forming processes

shown in Fig.2[7]，when make briquette by using bituminous coal, anthracite and the old lignite,

there are some difficulties if we make briquette only by use molding pressure alone. Thus, there

require incorporation the binder in the raw coal to improve the plasticity and adhesion. So there

require incorporation the binder in the raw coal to improve the plasticity and adhesion. [2].

Fig.3 shows the non-adhesive forming process [7]. In the process of non-adhesive formulations,

the coal, coal type, coal viscosity, water content, pressure forming, pressure forming speed and time

are the main process parameters. Such as the water in coal generally require 6% to 10%. If moisture

content is too little, excessive consumption molding pressure; if the moisture content of coal is too

much, there will affect the strength of coal.

Fig.2 Adhesive molding process

Fig.3 Adhesive-free molding process

Applied Mechanics and Materials Vols. 178-181 99

2) Additives

During the industrial coal forming process, the most important is the desulfurization agent.

When coal combustion，desulfurization agent and released SO2 react into sulfate，and fix in the coal

ash. Most agent is a calcium-based desulfurization agent. Mechanism shows in followed

sulfur-type:

The sulfur effect of coal briquette is affected by many factors. In order to achieve better

desulfurization results, some factors must be account as follows:

a) choose minimize size desulfurization agent: the smaller particle size, its surface area will

greater, and it is also easier to react with SO2. However, we should consider the balance of reducing

additive particle size and increasing processing cost.

b) Ca/S ratio is the most significant factor of desulfurization, which reflects the added amount

of calcium-based desulfurization agent. Excess desulfurization agent can achieve a better effect of

sulfur. However, added the desulfurization agent will increase coal costs and the ash content of coal,

which will reducing fixed carbon content and calorific value. Generally, the appropriate Ca/S ratio

is 1.5 to 2.

c) Sulfur temperature: CaSO4 is the sulfur product of a calcium-based desulfurization agent.

The more CaSO4 generate in the coal combustion ash, the effect desulfurization agent is better, but

CaSO4 will decomposition when the temperatures above 1350℃. Therefore, in order to ensure a

certain degree of desulfurization rate , appropriate desulfurization temperature is 800℃~ 1000℃[8].

3) Biomass briquette technology

The biomass briquette composition includes broken into a certain size, drying to a certain

degree of coal and combustible biomass, a certain percentage of mixing, adding a small amount of

desulfurization agent,

Biomass briquette characters are low moisture, high volatile easy to precipitate volatile, fire

and ignite permeability, easy storage and transportation. And during the combustion process, there

can form pores to improve coal combustion, sulfur rate and reduce the amount of generated dust. In

addition, due to the organic biomass burning off early than coal, the gap left after carbonization will

play a role of extruded loose, increase the diffusion of SO2 and O2 within the CaO particle. In

addition, because the desulfurization agent mixed well, the desulfurization rate of biomass briquette

can achieve 50% under a lower Ca/S ratio, which is higher than normal coal [9-12]

.

4) Application

A new type of coal briquette has been successfully used in the flue-cured tobacco furnace in

China's Hunan Province, which was co-developed by Huazhong University of Science ＆

Technology and Hunan Ruihe company. This plant-specific environmental clean coal compositions

include the coal(83%), sulfur agent and accelerant (3%), tobacco stems or stalks(10%), coal

binder(4%). According to test results, diameter 3cm round pie has a best combustion performance in

the metal chamber. The shape has a thin edge and thick middle, shown in Fi.4.

Fig. 4 Coal briquette products Fig.5 Burning improved-coal

100 Sustainable Environment and Transportation

The molding pressure of this briquette is 500Mpa, good advantages as follows: (a)

significantly reduce dust emissions and deposition, maintain a high heat transfer efficiency, so as to

can achieve energy-saving purposes; (b) reduces nearly 90% of the sulfur dioxide emissions; (c) use

special adhesive to replace traditional clay, improve coal combustion and high temperature strength,

shown in Fig.5. Therefore, this briquette worth our to promotion and large-scale application.

Conclusions

China has more than 50 million units coal-fired boilers, which annual emission a large number

of of SO2 and dust to the atmosphere. How to control a large number of industrial boilers sewage

problems related to the healthy development of China's national economy. According to the text

analysis, clean coal briquette technology can largely resolve the problem of industrial boiler

emissions, improve the combustion characteristics and efficiency of coal-fired boilers. And also will

in line with China in the future for coal as a long time primary energy conditions. Therefore, coal

briquette technology has broad development prospects in China.

Acknowledgement

This work was financially supported by the Natural Science Foundation (51076057).

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