CN1250079A - High-efficiency and low-pollution fuel coal and its making process - Google Patents

Abstract

The present invention relates to efficient low-pollution utilization of coal. Raw coal is treated through sieving, crushing, forming and mixing to produce coal powder of size smaller than x1 and fine grain coal of x1-x2 size. Before forming, the coal is sulfur fixing and modifying treated. Desulfurizer, adhesive, modifier, water reducing agent, setting accelerator and other additives and mixed coal are added into coal powder and through several stage mixing and extrusion, briquette is produced. The fine grain coal without powder and after sulfur fixing moldified and the briquette are efficient and low-pollution fuel coal and are suitable for use in laminar burning furnace and fluidized combustion furnace.

Description

High-efficiency low-pollution fuel coal and its production method

The invention relates to a high-efficiency low-pollution utilization of coal, which comprises industrial fuel coal: fine coal, industrial briquette and their production process and apparatus.

The present invention relates to a new-type fuel coal suitable for layer-type combustion kiln and fluidized-bed combustion furnace and its production method. Unless otherwise stated, the term "furnace" and "fuel coal" as used herein refer to both the aforementioned furnaces and their coals.

Coal accounts for about 70 percent of primary energy in China, and is consumed by more than 11 hundred million tons every year, wherein the coal for industrial boilers accounts for about 1/3. Nearly 50 million industrial boilers exist in China, most of the boilers are layer combustion boilers and boiling combustion furnaces, and if the boilers comprise layer combustion power boilers, gas generators and grate typeindustrial kilns, the annual coal consumption is more than 4 hundred million tons, and civil honeycomb briquette is added, the total amount of the fuel coal of the cover is about 7 hundred million tons.

The fuel coal utilization rate of China is very low, and the smoke pollution is serious. The authoritative department points out that: "the heat efficiency of industrial boiler is about 20% lower than that of developed country" in our country, "the smoke pollution of industrial boiler is serious, the carbon content of slag is over 8% of the national standard requirement", "the heat efficiency of industrial boiler is up to 80% by identification, but the heat efficiency of actual operation is not high", "countries spend a lot of manpower and material resources for many years, the result of … … is not satisfactory when the research is carried out in this respect", etc. (refer to data retrieval catalog 1). The design and manufacturing guidelines of industrial boilers in China are as follows: "adapt to various coal types with various varieties", the strength is focused on the improvement of combustion technology and combustion equipment, and the result is half a success. Under the conditions of long-term planned economy and seller market in the coal-carbon industry, the fuel coal supply is dug yarn and sold yarn, which is not reformed so far. So that the heat efficiency of industrial boilers in China still stays at a low level of 60-65% till now, wherein the heat efficiency of anthracite furnaces and small-sized furnaces is even lower than 60%. If 75% is taken as reasonable thermal efficiency, the coal carbon is wasted by 7000 ten thousand tons per year for one industrial boiler, and the value is nearly 200 million yuan.

Based on the fuel coal consumption of 7 hundred million tons and the average sulfur content of 1 percent, the SO is discharged every year₂The acid gas reaches 1400 million tons, and becomes the largest air pollution source inChina. The number of combustion furnaces in China is very large, the distribution is wide and scattered, although the flue gas desulfurization technology is mature, the investment is large, the operation cost is high, except that the flue gas desulfurization device is additionally arranged on the gas producer, most furnaces have no capacity to use the technology at all, and the civil coal desulfurization is a blank. Cause acid rainThe public nuisance is becoming more and more serious. The state has recently determined to sign SO₂The emission cost and the shutdown of the high-sulfur coal mine can be seen, and the fuel coal acid gas pollution is severe.

Coal-carbon variety and existing fuel coal property

1. Coal particle size variety: the raw coal is screened and processed into three categories of 12 varieties according to the particle size (namely the sieve pore size), and the particle size is d^mm. Wherein the coal blocks are 7 varieties, and d is more than 13^mm(ii) a 1 variety of granular coal, d is 6-13^mm(ii) a 4 kinds of coal powder mixed, d is 0-X^mmNamely:

1) pulverized coal: d is 0 to 6^mm2) And (3) pulverized coal: d is 0 to 13^mm

3) Mixing the pulverized coal: d is 0 to 25^mm4) Mixing coal: d is 0 to 50 or 0 to 100^mm

Most of medium and small coal mines are simply selected and sold together with mixed coal.

2. Coal quality variety of coal: volatile matter V based on combustible base of coal^r(%) and colloidal layer thickness y (mm) fall into three series of ten major categories, namely: anthracite coal; bituminous coal (containing eight major classes) and lignite.

V of bituminous coal and lignite^rHigh combustion performance. The Y value represents the coking property of coalWhen the value of Y is too high, the combustion performance is affected. Anthracite (V)^rLess than or equal to 10 percent, and Y is 0) is a non-combustible coal.

3. Existing fuel coal property and fuel requirement of best working condition of combustion furnace

1) Grate-fired boiler (70% of them are stoker): d for combustion is 0-40^mmThe coal blend of (1), wherein d is 0 to 6^mmThe proportion of the powder is less than 55 percent. The optimal working condition requirement is as follows: d is 8 +/-2-20 +/-5^mm(the anthracite coal takes a small value), the phenomena of fly ash, coal leakage and cinder ladle carbon can be basically eliminated, and the coal bed is ensured to have good air permeability and enough combustion reaction specific surface area, so that the loss q is caused by incomplete mechanical combustion₄The coal saving rate is reduced by 7 percent, and the coal saving rate is over 10 percent.

2) Boiling combustion furnace: d for combustion is 0-8 +/-2^mmThe raw coal can meet the requirements only by screening, crushing and processing, and is generally processed by users. The fluidized bed furnace can stably burn any inferior coal, the burning efficiency of the particles which can be stabilized in the fluidized bed can reach more than 98 percent, and the q of the fluidized bed furnace₄Heat loss is almost concentrated on fly ash losses. Therefore, the optimum particle size range is: d is 1-8 +/-2^mm. Selection of d_min≈1^mmIt can eliminate all the primary fly ash and most of the burning-shrinkage fly ash, and reduce the fly ash amount by over 80% and save coal by over 20%.

3) A gas producer: lump coal, lump coke or machine-made briquette (mainly lime carbonized briquette) for existing combustion.

4) Other grate type industrial furnaces: mixed coal or lump coal for combustion.

5) A household furnace: the honeycomb briquette is made by mixing powdered coal and slack coal with more than 20% of clay. The amount of solid waste is large.

(Classification of coal and reference to coal Properties of Fuel: reference data search Cat 2, P3, 12; Cat 3, P13; Cat 4, P13, 203)

The powdered coal mixture is the main fuel coal and has a granularity d ranging from 0 to X^mmI.e. coal containing fines, for different combustionIn the furnace, the particle size ranges of the powder crumbs are different, namely the maximum particle sizes of the powder crumbs are different. For example, in a fluidized bed furnace, the particle size of the powder is d in the range of 0 to (0.5 to 1.0)^mm(ii) a For a grate-fired boiler, the particle size of the powder is d 0-6^mm. The raw coal in China has a large proportion of fines content, and generally: d is 0 to 0.5^mmThe proportion of the components is 20-35%; d is 0 to 6^mmThe proportion of (A) is 50-60%. For the coal for the fluidized bed furnace, the content of the powder after crushing is larger.

The large content of coal dust is the main reason of low heat efficiency and large smoke dust of combustion furnace.

1. And (3) a layer combustion furnace: the dust causes poor and uneven air permeability of the coal seam, worsens working conditions, even causes local slag bonding and increases the air excess coefficient due to coal seam perforation. Thereby increasing heat loss q of exhaust smoke₂(ii) a Increase of chemical incomplete combustion loss q₃；d＝0～6^mmThe powder scraps are the source of fly ash and coal leakage, so that the incomplete combustion loss q of the machine is caused₄And is increased.

2. For a fluidized bed furnace: d is 0 to 0.5^mmThe dust in the fluidized bed can not be stably combusted, and all the dust becomes fly ash. d is 0.5 to 1.0^mmThe powder is formed into secondary fly ash due to burning and shrinkage, and the secondary fly ash is also thermally exploded. The secondary fly ash accounts for about 10% of the total ash content (ref. index No. 4, P203), with low combustible content of the burning-shrinkage fly ash and less impact on thermal efficiency. It can be seen that the pulverized coal dust is a major source of the fluidized bed furnace fly ash. In order to solve the problem of heat loss of fly ash, although China has tried for more than thirty years, a set of technical measures is formed and the effect is good, but the effect is not good in general popularization. Moreover, the technical measures do not cause the furnace body to be bulky and complicated in structure, and increase the construction investment and the heat dissipation loss q of the furnace body₅。

And the combustion efficiency is very low when the coal with too low volatile matter, too strong coking property and poor fixed carbon activity is used for the grate-fired furnace. The prior art countermeasures are only furnace-front mixing of bituminous coal or watering for improvement.

And the loss of the fuel coal in the operations of loading, transporting, unloading and storing is about 2-3%, and dust pollution is diffused to the whole process of coal utilization.

<five>Prior Art of desulfurization pretreatment of Fuel coal

Pretreatment of desulfurization with fuel coalThe application technology for solving the problem of flue gas desulfurization of the fluidized bed furnace is popularized abroad, and the key points of the technical scheme are as follows: (1) using CaO-rich ore (such as limestone and dolomite) as desulfurizer, and processing into powder with particle size d of 0-3^mmThe powder particles of (2) are put into a furnace together with coal; (2) and a recovery system is arranged to collect the mineral powder which is not fully utilized and recycle the mineral powder. It is generally required that the Ca/S equivalent ratio is not less than 2. Because of the large specific gravity of the ore, the volume share ratio of the desulfurizing agent in the fuel is generally lower than 2%, which makes the technology not suitable for the grate-fired furnace. The technology can lead the desulfurization rate of the flue gas of the fluidized bed furnace to reach more than 95 percent, and China also has research and test results but is not popularized (refer to data retrieval catalogues 5, P6-7, 11-13 and 39-41).

The powder-mixed coal desulfurization pretreatment technology for the grate-fired furnace is still a blank.

Sixthly, the technical current situation of the molded coal for the gas producer

The main varieties are: lime carbonized briquettes, pulp black liquor briquettes, cement briquettes, clay coal rods, clean water coal rods and the like. Only lime-carbonized briquettes have been widely popularized, but they also have major drawbacks, mainly:

1. the lime consumption is large, the adding proportion is higher than 20 percent generally, and the inferior coal even exceeds 30 percent, so that the fixed carbon content of the briquettes is greatly reduced, the gas preparation capacity of equipment is influenced, and the cost is increased. The reason is that lime has great influence on the ash melting point of coal and is in a saddle-shaped curve, when the lime addition meets the strength requirement of the briquette, the ash melting point is in a valley bottom area, and the lime dosage must be increased continuously to gradually increase the ash melting point. (refer to data retrieval catalog 6, P128-132) andash melting point is a crucial technical index for gas making process.

2. Low ash melting point, general softening temperature T₂1250-1300 ℃, which is the low limit of the gas making process requirement, limits the furnace temperature and reduces the thermal efficiency of the equipment.

3. The manufacturing process is long in flow and relatively complex. Lime is used as a binder, and CO is required to be introduced after forming₂Reacting Ca (OH)₂Reduction to CaCO₃Therefore, the processing energy consumption is large and the cost is high. And is not suitable for continuous large-scale productionAnd (4) producing.

The purpose of the invention is to:

the defects of the existing fuel coal are eliminated from two sources of coal and coal-carbon enterprises. Realizes the high-efficiency combustion of fuel coal and reduces SO₂Acid gas pollution and smoke pollution; the reasonable utilization of the coal is realized, the operation loss of loading, transporting, unloading and storing the coal is reduced, and the dust pollution surface is reduced. Thereby achieving the high efficiency and low pollution of the whole process of coal utilization.

In order to achieve the above object of the present invention, the following means is provided.

Technical scheme overview

According to the coal quality characteristics, the requirements of high-efficiency combustion process and the variety requirements of fuel coal in the market and according to the reasonable coal utilization principle of 'high-quality good use, low-quality application and flame-retardant modification', raw coal is screened, crushed, pulverized into powder and mixed to obtain the coal with the particle size range of d-0-X₁ ^mmThe coal fines and the particle size range ofd ═ X₁～X₂The coal pellets in (1) are referred to as fine coal pellets for use in a fluidized bed furnace and coarse coal pellets for use in a grate-fired furnace.

And carrying out desulfurization pretreatment and necessary modification treatment during the formation of the pulverized coal scraps. The coal powder is added with a certain proportion of additives such as desulfurizer, binder, modifier, water reducer, quick-acting agent, activator, antifreeze agent and explosion-proof agent and blended coal, and the mixture is continuously stirred and mixed in a segmented multistage sequential manner, and then is extruded and molded to obtain the product called briquette. Among them, the briquette is called a common briquette which is suitable for a grate firing boiler and a fluidized bed furnace; the coal briquette is suitable for gas generators and other furnaces which need high-strength high-quality blocky fuel and is called as gasified coal briquette; the semi-finished product which is only subjected to pre-desulfurization treatment and is stirred into particles is called civil coal.

The product obtained by mixing the common coal briquettes with different specifications or particle size ratios with coarse and fine coal is called type coal mixture. The proportion of the molded coal is more than 20 percent when the molded coal is used in molded mixed coal of a grate-fired furnace; the proportion of the molded coal in the molded coal mixture used for the fluidized bed furnace is more than 5 percent so as to ensure the desulfurization efficiency. When the fine coal is used as the fuel of the fluidized bed furnace, ore rich in CaO is added as a desulfurizer according to the desulfurization requirement.

The fine coal, briquette, coal mixture and civil coal are the fuel coal with high efficiency and low pollution. It is mainly characterized in that: no powder, pre-desulfurization, reasonable granularity range and grading, and improved combustion performance.

Use of slaked lime powder-Ca (OH)₂The important technical characteristics of the invention are that the desulfurizer can be used as a desulfurizer and also can be used as a briquette binder: the key of the invention is the briquette manufacturing technology.

<II>Ca(OH)₂Desulfurization mechanism, advantages and calculations.

1. The mechanism is as follows:

there are three states of sulfur in coal: volatile sulfur, combustible sulfur (mostly iron sulfide) and fixed sulfur, which exists as sulfate and remains in the slag after combustion. Sulfur is an extremely active element which can be sublimed at normal temperature, has a melting point of less than 120 deg.C, a burning point of less than 262 deg.C, and a chemical activity of greater than C, CO and alkane gases (volatile components of coal). When the coal is heated, volatile sulfur content is oxidized to produce SO₂And trace SO₃After the temperature is raised, the combustible sulfur content is decomposed and oxidated. Ca (OH)₂Is an alkaline substance which can react with SO at normal temperature₂The acid gas generates neutralization reaction. The temperature is increased, the reaction is accelerated to 580 ℃, Ca (OH)₂Decomposition into CaO and H₂And O, CaO continues to perform desulfurization reaction. The reaction formula is as follows:

； ； ；

generated calcium sulfite CaSO₃Further oxidized to CaSO under high temperature conditions₄Calcium sulfate is a stable, harmlesssalt; the calcium sulfate is fixed in the slag, and the calcium sulfate has good coagulation property, thereby being beneficial to the comprehensive utilization of the slag.

2. The advantages are that: with limestone-CaCO₃As compared with the desulfurizing agent, the present invention has the following advantages.

1) The specific surface area of the desulfurization reaction is large, and the reaction speed and the utilization rate of the desulfurizer are improved.

The desulfurization reaction is a gas-solid heterogeneous reaction, which occurs on the surface of a solid, so that the reaction rate is positively correlated with the total surface area of the solid. For a given amount of solid, its total surface area and specific surface area (M)²/Kg) is in direct correlation and the specific surface area is inversely proportional to the square of the mean diameter of the solid particles. Ca (OH)₂In the form of naturally dispersed micropowder with micron-sized particle diameter, and CaCO₃The mineral powder has an average particle size of millimeter, so that the difference between the specific surface areas is more than thousand times. Meanwhile, Ca (OH)₂The micro powder is uniformly distributed in the molded coal, and the ratio of the molded coal in the molded coal mixed for the grate-fired furnace is up to more than 20 percent, so the desulfurization reaction probability is greatly increased.

2) The desulfurization reaction temperature range is large, the activity is strong, and the combustion condition can be improved by the reaction by-product water vapor.

As described above, Ca (OH)₂Is alkaline matter and can react with acid gas at normal temperature. In contrast, CaCO₃Is a neutral salt, and decomposes into CaO and CO at 825 deg.C₂CaO canstrongly exert a desulfurization effect. Ca (OH)₂The low-temperature desulfurization characteristic is significant for the grate-fired furnace, and the common grate-fired boiler, such as a chain furnace and the like, has a preheating ignition region in a coal seam, has low temperature, but volatile sulfur is concentrated and separated out, Ca (OH)₂Synchronous desulfurization can be ensured. On the other hand Ca (OH)₂The by-product of the reaction is steam, and the reduction reaction activity of the steam on carbon is CO₂Three times of the catalyst is the catalyst for the oxidation reaction of CO and alkane gases, so that the combustion condition can be improved, the chemical incomplete combustion loss is reduced, and the carbon combustion is accelerated. (Special remarks below)

3)Ca(OH)₂Is an excellent adhesive, has the functions of lubrication and plasticization, and is beneficial to the forming process.

3、Ca(OH)₂And (3) calculating the addition amount: molecular weight: s-32; ca-40

Setting: the amount of pulverized coal scraps is 100 percent; the equivalent ratio of Ca/S is r;

the sulfur content of the coal is S%; the calcium content of the slaked lime is Ca%; the proportion of the molded coal in the molded mixed coal is Y percent. Then:

description of the drawings: 1) determination of the equivalence ratio r: common briquette coal: r is 1.2 to 1.5; civil coal feed: and (r) 1.5-2 (high sulfur concentration value) of gasified briquette: the smaller value of r is 0.5-0.8 r is because the main reaction of the gas producer is gasification reaction, and the generated sulfide H₂S, cannot be removed with CaO. At the same time, CaO lowers the ash melting point, which has an adverse effect.

2) When the coal contains CaO,the CaO is regarded as an inherent desulfurizer, and the calculation can be carried out according to the reduction.

Technical key field for manufacturing briquette

1. Technical requirements of the briquette

1) Cold mechanical strength: meets the requirements of loading, transporting, unloading and storing operations, and is expressed by the crushing rate k, namely, the proportion of the crushed crumbs generated by freely dropping a certain amount of the briquette on a hard surface from 2m height. For common briquettes: powder d is 0 to 0.5^mm(ii) a For the gasified briquette: 0 to 10% of powder^mm. The method comprises the following steps: common briquette coal: k is less than 5 percent; gasifying briquette coal: k is less than 10 percent, and the compressive strength of the single ball is more than 5 MPa.

2) Water resistance: the water can not be well soaked.

3) Meets the pre-desulfurization requirement of the fuel coal.

4) Thermal stability:

a. ash fusion point T₂: gasified briquette T₂More than 1350 ℃; common briquette T₂The reduction rate is less than 10%.

b. Heat strength: at 1000 ℃; the common briquette is not pulverized and can be sintered; gasifying briquette coal: the single sphere strength is more than 1 MPa.

5) The condensation property and the quick setting property: and (4) condensing at room temperature, and finishing primary and final condensation within 3-5 minutes.

6) The additive is non-toxic and easy to obtain, and does not produce additional pollution during combustion.

2. The formula design of the admixture is as follows: the recipe is listed in table 1.

The admixture technology is developed comprehensively based on the mature technology of cement concrete admixture (reference data retrieval catalog 7) and the new technology of unshaped refractory material (reference data retrieval catalog 8, chapters 3, 4, 7, 8 and 11) according to the combustion characteristics of coal, the technical requirements of briquette coal and different combustion furnace process conditions.

1) Slaked lime powder: the amount of addition is calculated as described above, and the lime should be sufficiently digested with particular attention to prevent the quicklime component from mixing into the briquette to cause decrepitation.

2) Cement: the high-performance condensation type binder ensures that the molded coal has good water resistance and cold strength. High alumina cement (i.e., alumina cement) is also an excellent refractory material, which can increase the ash melting point of coal, but is expensive and is only used for gasification of briquettes.

3) Soft raw clay powder: a binder and a coal conditioning agent.

The method has important significance for the manufacturing technology of the molded coal, the chemical components, the fineness, the plasticity, the sintering property and the refractoriness of the soft clay. Generally, common clay can be selected for common coal, and for coal for a fluidized bed furnace, the common clay with good sintering property and low sintering temperature is selected to improve the thermal stability and the thermal wear resistance and scouring resistance of the coal briquette so as to adapt to the special working condition of strong movement of furnace charge particles; for coal for a grate-fired furnace with a low ash melting point, clay with a high refractory temperature should be selected.

The gasified briquette must use refractory grade soft clay, and the requirements are as follows: al (Al)₂O₃＞28％，Fe₂O₃Less than 2%, the fire-resistant temperature is more than 1700 ℃, the fineness is as follows: d is less than 5 μm and accounts for more than 50 percent.

4) Water usage and the significance of steam in coal combustion.

The research of the combustion science shows that (refer to the data retrieval catalog 9, P7-14, 123-159), the existence of proper amount of water vapor has great significance for improving the working condition of the combustion furnace: (1) steam is a combustion catalyst for CO and alkane gases. The water vapor content in the flue gas is directly proportional to the CO oxidation rate. When the water-carbon ratio (total carbon of carbon-based combustible gas) in the flue gas reaches a certain value, the combustible gas can be ensured not to have disproportionation and degradation reaction, carbon precipitation, namely black smoke phenomenon is prevented, and the chemical incomplete combustion loss is reduced. The smoke coal furnace usually adopts steam secondary air or coal before the furnace is watered, namely, the smoke coal furnace is sourced from the steam secondary air or the coal before the furnace is watered; (2) the carbon burn-off is effected, in a sense, by reduction in which the reducing reactant is mainly CO₂And H₂O, but water has a small molecular weight and is therefore strongly reactive, and is CO₂3 times of the total weight of the product. Due to the raw coal

TABLE 1 formular coal blending agent prescription table

Variety of food	Act on	Common briquette		Gasified briquette		Note that
							Require that	Dosage of	Require that	Dosage of
		Slaked lime powder	Desulfurizing, binding, plasticizing and moistening Slippery and activePromoting coagulation	Fully digested and loosened Fineness: 100 mesh	Computing						On the same left	Computing
Cement	Bonding, condensation and water resistance					425# and above common type	1-2% of coal powder	525# high-alumina cement	1-2% of coal powder
		Soft raw clay powder	Binding, plasticizing, lubricating, firing Bind, adjust T, reduce coking	Of ordinary or refractory grade Fineness: 100 mesh dry powder	3 to 6 percent of coal powder						A high-aluminum low-iron refractory grade, fineness: 100 mesh dry powder	3 to 5 percent of coal powder
Water (W)	Binding agent and improving working condition					Natural purified water with pH > 4 or Industrial water	Meet the requirement of forming process	On the same left	On the same left
		Cement water reducing agent	Dispersing, lubricating, moistening and increasing Moulding, reducing water and improving strength	General type	Cement and clay 0.4～1.0％						High efficiency type	On the same left	Reference to product description
Cement accelerator	Quick setting and early strength improvement					Initial setting: 2-3 min Final setting: 4-5 min	2 to 4 percent of cement	On the same left	On the same left	Reference to product description
		Antifreeze agent	Anti-freezing	Selecting and using a shaped product	According to the instruction						On the same left	On the same left
Industrial NaCl	Carbon activator, anti-freezing and coagulation-promoting					For very low VT only Anthracite for grate-fired furnace	Coal powder 0.1～0.3％
		Explosion-proof agent	Preventing high temperature bursting								Polystyrene short fiber paper Pulp fiber	1 to 2 percent of cement	The thinner the herb is, the better the herb is
Cement separating agent	Preventing adhesion before coagulation of briquette					Selecting and using a shaped product	Micro amount of spraying

Most of the water is external water and is quickly diffused in the preheating and drying stage, and the formed coal contains cement crystal water, adsorbed water and Ca (OH)₂The chemical diving temperature is 200-600 ℃, the desorption and separation or decomposition and emission temperature is almost synchronous with the volatile matter separation, the excessive concentrated separation of the volatile matter can be effectively inhibited, and partial water vapor can accelerate the reduction reaction of carbon through a scorching carbon zone. Therefore, under the condition of ensuring the molding process, purposefully improving the water content of the molded coal is the most economic technical measure.

5) Cement water reducing agent: has the functions of dispersing, lubricating, wetting and plasticizing cement, clay and pulverized coal scraps, and is the most important auxiliary agent for ensuring stirring, mixing and forming processes. Meanwhile, the cement strength is improved by 20-50%, or the cement dosage is reduced, and the water adding weight is reduced. The water reducing agent has a plurality of varieties, is divided into a common type and a high-efficiency type, has the national standard, and is selected according to a product specification, and the quantity of cement and clay is taken as the reference when the weight is calculated.

6) Cement accelerator: the method can ensure that the initial setting and the final setting of the briquette can be realized within 3-5 minutes, and is a necessary condition for centralized processing and large-scale operation.

7) With respect to the combustion activity of coal and combustion activator of carbon: the combustible base of the coal comprises volatile matter V^rCarbon of Heguo nationality^r。V^rThe higher the value, the better thecombustion activity of the coal, combustion V^rThe low volatile matter anthracite layer combustion boiler with less than 5 percent has extremely low thermal efficiency and needs to be subjected to blended combustion treatment to ensure that the molded coal V^rNot less than 10%. Generally selected from V^rMore than 35 percent of high volatile bituminous coal is mixed burning coal.

The fixed carbon exists in a crystal form, has weak combustion activity, and is difficult to catch fire and slow to burn when the volatile matter is low. When the coal ash contains oxides or salts of K, Na, Ca, Fe, Mn, Ni and other elements, the substances can distort crystal lattices of fixed carbon under high temperature, improve the oxidation and reduction activities of C and accelerate the combustion of C, and particularly the K, Na compound has the strongest effect. Therefore, industrial NaCl is selected as an anthracite activator (only used for grate-fired coal). (reference retrieval catalog 9, P137 to 138)

8) The antifreeze is only used for freezing temperature conditions; the explosion-proof agent is used for improving the quality of the gasified briquette; the cement isolating agent is used for preventing adhesion after the molding of common briquette.

9) Care must be taken to influence the effect of the admixture on ash melting point: the ash fusion point of coal varies greatly with coal, and its softening temperature T is large₂Low only 1000 deg.c, high above 1500 deg.c. In general, K, Na, Ca, Fe and other elements lower the ash melting point, while Al₂O₃And SiO₂Increased contentThe ash melting point will increase. The ash melting point index is crucial to gasified briquette, some of the additives are Na and Ca agents which are avoided as much as possible, and high-alumina clay is selected, so that the gasified briquette T is obtained through experiments₂The temperature is higher than 1450 ℃, which can make the heat efficiency and productivity of the gas producer obtain a great breakthrough.

10) Some admixtures have an inhibitory effect on each other, for example: calcium ions can inhibit the effect of the sodium ion type water reducing agent, so that the process of the admixture contains an admixture program design and needs multistage mixing and stirring in stages.

11) Some admixtures are multifunctional (as shown in table 1) with mutual substitution, such as: when the lime is used in a larger amount, the clay amount can be reduced.

12) The plasticity of the coal dust greatly affects the forming process, thereby affecting the proportion of the binder. Thus, the admixture formulation design is determined under conditions of coal quality analysis, admixture selection and experimental optimization.

3. The manufacturing process of the briquette has the design points that:

the process flow diagram is shown in figure 1 (taking anthracite as an example).

Description of the drawings:

1) a charging process:

a. the feeding equipment should be metered and continuously adjustable.

b. The water-soluble admixture is prepared into a hydrosolvent, and more than 80 percent of water consumption is applied to preparing the water reducing agent. The solvent spray head adopts a film type or a fog type.

c. The order of addition should be arranged according to the design program of the formula of the admixture.

2) Mixing and stirring: the dosage of the admixture is small, and is only ten-thousandth, and the key for ensuring the quality of the molded coal is to realize the sufficient, uniform and continuous mixing of the materials. Therefore, various measures such as premixing, dilution, segmentation, multistage and the like are adopted. The general main flow should be: first-stage dry mixing, second-stage wet mixing and third-stage wet mixing, wherein each stage of stirring machinery is required to ensure that the material stirring travel time is not less than 2 minutes.

3) A molding procedure: an extrusion forming process is adopted.

a. Designing the granularity of the briquette: design typeThe size of the cross section of coal is a x b^mmLength of 1^mm。

Then: coal for grate-fired furnaces: a is 8-10; b is 15-20; 1 is 30-40; the lower limit of anthracite is taken.

Coal for fluidized bed furnace: a ═ b; 1 is 5-8. The value of a should have at least 3 specifications corresponding to an opening ratio of phi. Namely: a is₁＝2，φ₁≈50％；a₂＝2.5，φ₂≈30％；a₃＝3，φ₃20% is approximately distributed. To ensure a reasonable grading of the fuel particle size.

Gasifying briquette coal: the ball equivalent diameter of the existing shaped briquette machine is about 25^mm。

b. The quick setting process comprises the following steps: the initial setting of the extruded material and the final setting of the briquette before warehousing are ensured, i.e. the initial setting and the final setting of the briquette are completed on the conveyer belt, and the linear speed of the conveyer belt of the briquette is continuously adjustable.

c. The speed of the forming machine is continuously adjustable, and the material balance of the system is ensured.

d. Anti-sticking measures: the cement isolating agent is sprayed at the discharge port of the forming machine for the common briquette.

e. Production of molded coal mixture: the granulated coal is continuously added on a briquette conveying belt according to a certain proportion and put into a bin together.

f. Curing the molded coal: and (5) drying the gasified briquette at room temperature for 24 hours.

4. Master selection and special technical requirements:

1) the stirrer: the continuous feeding mode adopts a double-shaft stirrer. The surface of the machine part contacting with the material should be corrosion-resistant and wear-resistant, and the machine body should be provided with a sampling opening and a discharge opening which can be opened and closed safely and quickly.

2) A forming machine: the common briquette uses screw extruder or roller pellet press, and the gasified briquette uses roller pellet press (existing shaped product). The requirements of wear resistance, corrosion resistance and material opening are the same as those of a stirrer.

The screw extruder is a modification of the existing clay screw extrusion brick making machine, and the design and modification key points are as follows:

a. the sections of the casing should be connected by flanges.

b. The extrusion linear speed is controlled to be 8-15 cm/S, and a synchronous splitter is arranged at an extrusion opening.

c. Opening a hole at an extrusion opening: the longitudinal and transverse cutters with acute angle are embedded into a grid-shaped extrusion head, and the grid-shaped extrusion head is connected with the outlet of the extrusion section through a flange so as to be replaced at any time. The required briquette specification is obtained by different grid sizes.

Compared with the prior clean fuel coal technology, the invention has the following advantages.

Feasibility of coal reforming

1. The technical feasibility is as follows: the technical scheme covers 60 percent of the coal yield in China, can adapt to any change of coal quality and product requirements, is simple and feasible, and is beneficial to centralized processing, social service and reasonable utilization of coal; most of the equipment is a shaping or universal product; the process is reliable; the admixture is easy to obtain, non-toxic and free of additional pollution.

2. Economic feasibility: the coal improvement has the double meanings of energy saving and environmental protection, the investment of technical improvement is low, the investment of a million tons/grade processing system is estimated to be 10 yuan/ton, and the investment of a ten million tons/grade processing system is estimated to be 20 yuan/ton. And the processing cost is low, about 10 yuan/ton of molded coal is mixed, about 30 yuan/ton of gasified molded coal is mixed, and about 5 yuan/ton of civil feed coal is mixed. (see seven herein for example) so that the product has strong competitiveness.

And secondly, coal enterprises and social and economic benefits are great.

The coal is subjected to powder removal, granulation and modification, the optimal granularity range and grading are realized, the combustion efficiency can be generally improved by 10-20%, the operation loss can be reduced by 2% through centralized processing, the reasonable utilization of the coal is ensured, and the comprehensive coal saving rate is over 20%. Based on industrial boilers alone, the annual coal saving is about 7000 million tons, the value is close to 200 million yuan, and 1/3 can be returned to coal enterprises. Meanwhile, the coal saving and pollution reduction do not need the investment of users; the operation cost is reduced; the load of the dust remover is reduced, and water and electricity are saved; the product is gravel-shaped, has good water permeability, is not afraid of wind and rain, and can be stacked in the open air. Therefore, the method is beneficial to users and harmless, and has great social and economic benefits.

And thirdly, the method solves the pollution problem of industrial kilns and civil stoves in China.

1. As mentioned before, flue gas desulfurization technology is absolutely not economically feasible for medium and small kilns and domestic stoves. Therefore, the desulfurization pretreatment of the fuel coal becomes the only way. Moreover, the centralized desulfurization pre-treatment of the present invention is almost free to the user.

2. Desulfurization by-product CaSO₄Is harmless salt and can improve the comprehensive utilization value of the slag. Meanwhile, the method overcomes the defect that SO is treated by adopting a wet dust collector in large quantity at present₂Serious defects that water source and soil are polluted by the acid liquor.

3. The sanitary environment of families and towns is optimized, and the amount of solid garbage is reduced.

<fourth>post-technical ductility: the reformation of fuel coal can promote the birth of a new-generation boiler, realize the upgrading and updating of the coal-fired industrial boiler in China, and provide conditions for the development of a large-scale power furnace for the boiling combustion technology (low-temperature thorough burning, adaptation to any coal types, simple desulfurization technology and low NOx emission).

And fifthly, the method is favorable for economically controlling private excavation and random mining and private 'chicken nest mining' of individual households existing in the coal mining industry of China at present. The reason is that: coal processing systems that are too small are not cost effective in investment, and as coal currently forms the market for buyers, raw coal sales will gradually lose competitiveness.

The following examples will further illustrate the invention

The application principle of the invention is as follows: planning according to local conditions and overall planning. The 'coal change' plan of a million-ton anthracite coal mine is taken as an example for illustration.

<first>Scale: 100 million tons per year, II-class anthracite coal is located in unfrozen areas in the south of the Yangtze river and is sold together with raw coal at present.

And secondly, market product requirements are as follows:

1. coal for a grate firing boiler: more than 40 ten thousand tons;

2. coal for a boiling combustion boiler: more than 30 ten thousand tons;

3. raw materials of small nitrogenous fertilizer plants and coal for porcelain kilns: 15 ten thousand tons;

4. civil coal: more than 15 million tons.

<III>analysis of raw materials

1. Analysis of raw material coal: the method comprises the steps of industrial analysis, element analysis, ash component analysis, ash melting point determination, lump coal thermal stability test, pulverized coal scrap plasticity determination and raw coal screening test. The main results are as follows:

1) raw coal working base fixed carbon C^y70 percent; s% of sulfur content is 0.4%

Volatile component V of combustible base^r2 percent; melting point T of powder dust₂＝1350℃

2) The lump coalhas low thermal explosiveness and can meet the requirements, so the lump coal is selected.

3) Raw coal screening test and analysis: as listed in the following table:

particle size dmm	0～1	1～6	6～15	d＞15
									d＞30 Lump coal	Miscellaneous block			Total up to
				Before crushing	After crushing
							0～1	1～6
					The proportion of the components is%	40				20	20	5		15	3	12	100％
Fixed carbon Cy％	73	70	68	78			62	65	61.3				Average is 70%

4) Blended coal analysis: let V^r＝35％(d＝0～6^mm): s% ═ 2% 5) slaked lime powder analysis: setting Ca (OH)₂95% calcium content 51.4% 6) clay analysis: chemical composition, plasticity, sintering temperature, refractoriness and fineness. (IV) raw material coal distribution and product design principle: high quality and high use, low quality and applicability, modification and utilization, and reduced crushing processing amount. 1. Lump coal: 5 ten thousand tons, is used for porcelain kiln (d is more than 30)^mm，C^y78%), 2, gasification briquette raw material: 10 ten thousand tons (d is 0 to 1, C)^y73%), 3, grate-fired boiler feed: 40 ten thousand tons, wherein: 1) the briquette raw materials: the coal is counted by 20 ten thousand tons, and accounts for 50 percent of the coal mixture.

Powder scrap: 15 ten thousand tons (d is 0-1, C)^y＝73％，V^r＝2％，S％＝0.4％)

Blending and burning coal: 5 ten thousand tons (d is 0-6, V)^r＝35％，S％＝2％)

Calculating to obtain briquette V^r10.6% 2) coarse coal: 20 ten thousand tons (d is 6-15 mm, Cy is 68%, S% = 0.4%)

Then: the average sulfur content S% of the molded mixed coal is 0.6% 4, and the raw materials for the fluidized bed furnace are as follows: 35 ten thousand tons, wherein: 1) the briquette coal comprises the following materials: 3 ten thousand tons (d is 0-1C^y65%) accounting for 8.6% of the briquette. 2) Fine coal particles: 32 ten thousand tons (d is 1-6 ═ d^mmAverage of C^y66.7%) where: a. pure screening of coal: 20 million tons (C)^y70%) b, crushing and screening: 12 million tons (C)^y61.3%), 5, civil coal: 15 ten thousand tons (d is 0-1, C)^y＝73％)<Five of them>The formula design and the expense measurement of theadmixture are as follows: for example, table 2 is described below. 1. The amount of desulfurizing agent was calculated as described above. 2. The water loading is based on suitability for the molding process, as noted above.

TABLE 2 formula of coal blending agent and charge measuring and calculating table

Name of article	Shaped coal for grate-fired furnace						Briquette for fluidized bed furnace					Gasified briquette
																	Specification or Require that		Dosage of ％	Dosage of Kg/T coal	Unit price of Yuan/Kg	Amount of money Meta/T coal	Specification or Require that	Dosage of ％	Dosage of Kg/T coal	Unit price of Yuan/Kg	Amount of money Meta/T coal	Specification or Require that	Dosage of ％	Dosage of Kg/T coal	Unit price of Yuan/Kg	Amount of money Meta/T coal
	Slaked lime	Degree of purity 95％		Coal in coal 3.5	35	0.20	7.00	Purity of 95％	Coal in coal 13.6％	136	0.2	27.20	Degree of purity 95％	Coal in coal 0.8	8	0.20																	1.60
Cement																	Pr425 # Pra 425		Coal in coal 1.0	10	0.30	3.00	Pr425 # Pra 425	Coal in coal 1.5	15	0.30	4.50	High alumina 525	Coal in coal 2	20	0.60	12.00
	Clay clay	Yellow mud		Coal in coal 2.0	20	0.05	1.00	Yellow mud	Coal in coal 2.5	25	0.05	0.75	Refractory grade	Coal in coal 4	40	0.20																	8.00
Water reducing agent																	General type		Occupies water Soil plus earth 1.2	0.4	2.5	1.00	General type	Cement of + 1.0 of soil	0.40	2.5	1.00	High efficiency type	Occupies water Soil plus earth 1.0	0.5	3.0	1.50
	Accelerating agent	Red Star 1#		Coal in coal 2	0.2	2.5	0.50	Red Star 1#	Occupies water Mud 2	0.3	2.5	0.75	Red Star 1#	Occupies water Mud 2	0.4	2.5																	1.00
Activating agent																	Industrial process NaCl		Coal in coal 0.2	2	0.20	0.40
	Explosion-proof agent												Polyphenyl pipe Fiber	Occupies water 1.0% of mud	0.2	15																	3.0
Release agent																	Self-selection					0.50					1.00
	Total (Yuan/ton coal)			13.40				34.45					27.10
The increase rate of the ash content of the briquette coal is 6.1 percent																		14.6％					6.4％
							The cost of the briquette coal is 12.58 yuan/ton							29.42 yuan/ton														25.37 yuan/ton
Ton type coal mixture		Ash increasing rate 3.05%, total cost 6.30 yuan/ton																	Ash increase rate 1.3%, total cost; 2.50 yuan/ton
							Note that		Civil coal feed: 1.5% of lime, 3-5% of yellow mud and 2% of clay added as a dispersant (water reducing agent), and calculating the coal blending agent cost: 6.0 yuan/ton.

3. The briquette proportion of the briquette for the briquette mixing furnace is low, so the lime consumption is large, the requirement of bonding strength can be met, and the clay consumption is small, so the sintering requirement can be met.

4. The admixture is available in the form of no package for cement to lower cost.

5. And (3) economic analysis:

1) the cost of the coal mixing for the grate-fired furnace is 6.3 yuan/ton, the ash increase rate is about 3 percent, the combustible base content reduction rate is very low, and the influence on the transportation cost is very small.

2) The cost of the coal mixing for the boiling furnace is only 2.5 yuan/ton, and the ash content is not increased basically.

3) Gasifying briquette coal: carbon content of raw coal C^yWhen the ash content is 73% and the ash content increase rate is 6.8%, the briquette C^y68%. The raw material such as lime-carbonized briquet contains lime 20%, and briquet C^y58% if converted to standard coal C^yIf 84%, the cost is: 31.34 yuan/ton of gasified briquette and 57.93 yuan/ton of carbonized briquette.

4) Processing civil coal: lime, about 3% of raw clay powder and a water reducing agent are added according to requirements, and the mixture is stirred into a powder by the first-stage stirring and used as a raw material of a town honeycomb briquette factory. The desulfurization cost is about 6 yuan/ton. But the amount of waste can be reduced by about 50%.

6. The design of the formula of the admixture needs to be screened and preferred through experiments.

And sixthly, the process flow of the coal processing system is briefly described.

The coal processing system consists of three parts of screening, crushing and sorting, a middle coal bunker (yard) and molded coal mixing and manufacturing. The process flow diagram is shown in figure 2.

1. Screening, crushing and selecting blocks: selecting and matching equipment loads, performing three-shift production according to 200 tons/hour, andmanually selecting blocks.

2. Intermediate bunker (yard): and (4) transitional storage, wherein the storage amount is 1-2 days of yield. The powder dust bin is a shed bin, and the pulverized coal is sprayed with water synchronously when being put into the bin to seep moisture and remove dust. The other storage bins are concrete plateaus.

3. Manufacturing of molded mixed coal: comprises 4 subsystems, namely 2 molded coal, 1 gasified molded coal and 1 civil coal.

1) Accounting for main equipment productivity of molded coal (three shifts, 300 days/year)

Common briquette coal: 23 ten thousand tons/year → 32T/H → 16T/station H

Gasifying briquette coal: 10 ten thousand tons/year → 14T/station H

Selecting: load capacity of a double-shaft mixer: 25T/H (non-standard, 10 stations in total)

Load capacity of screw extrusion molding machine: 25T/H (non-standard, 2 stations in total)

Load capacity of the roller-type briquette machine: 20T/H (finalizing, 1 station)

2) The screw extruder head design as described above, a common type of coal blending line can be used for different types of products.

4. Finished product warehouse, gasified molded coal drying, production monitoring, system dust removal and the like. Seventhly, the main equipment catalogue and the investment approximation calculation of coal change are as follows: the following table, excluding land use fees. Installation of unit price and sum of unit price of system name specification quantity

Ten thousand yuan (KW)1 crawler bulldozer 34.514 for sieving, crushing and coal feeding machine

Coal feeder vibrating feeder 1555

Three-layer screen vibration type 200T/H110105

Crusher jaw 400 x 30015530

Crusher roll 4PG 1151530

Double-layer screen vibration type 20T/H1331

Belt conveyor 105030

Others 18

Small counter 1201002, intermediate bin discharging and feeding machine loader ZL-50432128

Others 12

Small scale 1403, disk type feeder of coal mixing system, various specification 203040

Double-shaft 1010100170 of main mixer

Premixer twin shaft 35155

Spiral extrusion type 2102044 of forming machine

Roller type ball press 1151530 of forming machine

Belt conveyer etc. 4010

The subtotal 220300 equipment fee totals 480 ten thousand yuan installed capacity: the 400KW construction project cost is 200 ten thousand yuan water, electricity, biological control, dust removal and other 100 ten thousand yuan installation project cost 120 ten thousand yuan other 100 ten thousand yuan investment total: about 1000 ten thousand yuan capacity: 100 to 150 ten thousand tons/year. Therefore, the investment of coal reforming is about: 10 yuan/ton. The drawing figures are illustrated as follows: 1 disc feeder 9 three-layer screen 17 fine coal shed 2 belt conveyer 10 lump coal 18 fine particle coal yard 3 double-shaft mixer 11 crusher 11 lump coal yard 4 double-shaft mixer 12 double-layer screen 20, 21 common coal processing line 5 double-shaft mixer 13 crusher 22 gasified coal processing line 6 screw extruder 14 coarse coal 23 civil coal processing line 7 belt conveyer 15 fine coal shed 8 pit coal bunker 16 fine coal shed

Claims (5)

1. A non-powdered-dust pre-desulfurized fuel coal suitable for the layer-type combustion furnace and boiling combustion furnace to burn the mixed coal with 0-Xmm powder is prepared from powdered coal or raw coal through screening, breaking, shaping, mixing, desulfurizing and modifying while shaping₁～X₂The high-efficiency low-pollution fuel coal of the varieties such as mm fine coal, molded coal and the like is characterized in that:

firstly, the powder is not contained, and the particle size range meeting the requirement of the optimal working condition of the combustion furnace is as follows: namely, the particle size d which causes fly ash loss and coal leakage loss is less than X₁mm pulverized coal dust; the particle diameter d is larger than X and causes carbon-coated ash loss₂Large lumps of coal of mm;

secondly, the briquette has the function of a desulfurizer, and generates a desulfurization reaction during combustion to generate stable and harmless sulfate which is fixed in ash;

thirdly, the water-resistant and water-permeable fabric has good water resistance and water permeability and enough cold and hot strength;

fourth, the nonflammable coal types are improved.

Thereby realizing high-efficiency combustion of fuel coal and reducing SO₂Acid gas pollution and smoke pollution; the reasonable utilization of the coal is realized, the operation loss of the coal during loading, transporting, unloading and storing is reduced, the pollution surface of the coal dust is reduced, and the purposes of high efficiency and low pollution in the whole process of the coal utilization are achieved.

2. A non-fines, pre-desulfurized and modified fuelcoal according to claim 1 wherein the fine coal is a product of blending a proportion of an ore (e.g., limestone, dolomite) desulfurizing agent with a fine coal suitable for use in a fluidized bed combustion furnace.

3. A method for preparing pre-desulfurized coal briquette from pulverized coal scraps is characterized in that a certain proportion of desulfurizer is added into the pulverized coal scraps according to the characteristics of coal quality, the technical requirements of coal briquette quality and the economy of scale processing technology; a binder; dispersing, strengthening, plasticizing, lubricating, wetting agents; an accelerator; an anti-freeze agent; the admixture such as explosion-proof agent, carbon combustion activator and the like and the blended coal are sequentially added, fully and continuously stirred and mixed, and then are extruded and molded. The formula of the admixture is the core technology of briquette manufacture and is characterized in that:

first, use slaked lime powder-Ca (OH)₂As a desulfurizer and has the functions of bonding, plasticizing, lubricating and improving the carbon combustion activity;

secondly, using trace cement as a condensing adhesive to condense the molded coal at a warm condition and obtain water resistance and cold strength; the cement water reducing agent is used, and the functions of dispersing, plasticizing, lubricating and wetting cement, clay and coal micropowder are utilized, so that the forming process condition is improved, the cement strength is improved, and the cement using amount and the water adding amount are reduced; the cement accelerator is used, so that the complete final setting of the molded coal is ensured within 5 minutes, and the synchronous processing of molded coal manufacturing and molded coal mixing is ensured, so that the technical economy of large-scale continuous productionis adapted; an antifreeze agent is used to adapt to freezing climates;

thirdly, soft raw clay is used as a binder and a coal conditioning agent. The sintering property of the soft clay is utilized to enhance the thermal stability and the thermal scouring resistance of the molded coal; the high refractoriness of the high-aluminum low-iron refractory soft clay is utilized to improve the melting point of the molded coal ash;

fourthly, oxides or salts of potassium and sodium are used as combustion activators for the anthracite in the grate-fired furnace,

thereby ensuring the quality of the briquette and the manufacturing technology to be suitable for different coal quality and the technological requirements of a combustion furnace, and meeting the technical economy of centralized processing, large-scale production and low-cost operation.

4. The "admixture formulation" of claim 3, wherein: the formula of the gasified briquette coal blending agent with high ash melting point, high thermal stability, high strength and low ash content, which is suitable for a gas producer and the like, is as follows: high alumina cement (i.e., alumina cement); high refractoriness soft raw clay; a high-efficiency cement water reducing agent; cement accelerator, organic short fiber explosion-proof agent and low-limit consumption lime powder desulfurizer.

5. The "admixture formulation" of claim 3, wherein: the blending agent formula of a semi-finished product coal suitable for civil honeycomb briquette, which is called civil coal for short, is as follows: lime hydrate powder desulfurizer, common soft raw clay powder and water reducing agent.