Lime slaking slag caustic alkali recovery-thermoelectric flue gas desulfurization method

Abstract

The invention discloses a lime slaking slag caustic alkali recovery-thermoelectric flue gas desulfurization method which comprises the following steps: S10, preparing lime milk for alumina production by using a lime slaking machine, conveying the produced lime slaking slag to a slag washing machine through a slag extracting machine and a lime slag belt for washing, and overflowing and recovering the produced caustic alkali liquid for preparing the lime milk; s20, the washed lime slaking slag is smashed, and lime slaking slag powder is obtained; s30, blending the lime slaked slag powder with fire coal according to a certain proportion to form a mixed coal material, and feeding the mixed coal material into a thermoelectric coal-fired boiler for blending combustion for primary flue gas desulfurization; and S40, performing high-temperature dust removal on the flue gas subjected to primary flue gas desulfurization, and performing secondary flue gas desulfurization by adopting a lime powder-gypsum wet method. According to the method, the lime slaking slag caustic alkali can be effectively recovered and reutilized in thermoelectric flue gas desulfurization, the consumption of the caustic alkali of an aluminum oxide production system is reduced, and the limestone powder flue gas desulfurization cost of a thermoelectric coal-fired boiler is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of alumina production, and in particular relates to a method for recovering caustic soda from lime digestion residue and desulfurizing thermal power flue gas. Background Art

[0002] In the production of alumina, the traditional lime milk preparation process is to feed lime and hot water or flat Al(OH)3 washing liquid into the ash dissolving machine in proportion to prepare qualified lime milk for lime digestion. Since the lime kiln calcination process will produce lime to varying degrees of over-burning, the lime digestion slag rich in effective calcium will be discharged during the lime digestion process. Due to the lack of comprehensive recycling technology of existing lime digestion slag, it is generally transported to the red mud reservoir by car for mixed storage, and cannot be effectively or completely recycled and comprehensively utilized, resulting in waste of effective calcium or caustic soda in the alumina production system, and generates lime digestion slag storage and transportation fees and occupies limited red mud reservoir capacity. In addition, the lime digestion slag is easily weathered to produce dust, causing environmental dust pollution.

[0003] The alumina production system has its own coal-fired power plant. The lime powder-gypsum wet flue gas desulfurization process is widely used in flue gas desulfurization of coal-fired power plants due to its mature technology, high desulfurization efficiency, abundant lime powder sources, and usable by-product gypsum. However, it generally has problems such as high energy consumption and operating costs. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for lime digestion slag caustic soda recovery-thermal power flue gas desulfurization to solve the problem of how to comprehensively recycle the lime digestion slag.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for recovering caustic soda from lime digestion residue and desulfurizing thermal power flue gas, comprising:

[0007] S10, using a ash machine to prepare lime milk for alumina production, wherein the produced lime digestion slag is conveyed to a slag washer via a slag extractor and a lime slag belt for washing, and the produced caustic soda overflow is recovered for preparing the lime milk;

[0008] S20, crushing the washed lime digestion slag to obtain lime digestion slag powder;

[0009] S30, blending the lime digestion slag powder with coal in a certain proportion to form a mixed coal material, and sending the mixed coal material to a thermal power coal-fired boiler for mixed combustion to perform primary flue gas desulfurization;

[0010] S40, the flue gas after the primary flue gas desulfurization is subjected to high temperature dust removal and then the secondary flue gas desulfurization is carried out by lime powder-gypsum wet method.

[0011] Preferably, in step S20, the washed lime digestion slag is sent to a high-humidity material non-sieve bottom two-stage crusher through a chute to be crushed into lime digestion slag powder, and then transported to the lime digestion slag powder silo in the thermal power coal shed by belt conveyor or truck for storage.

[0012] Preferably, the particle size of the lime digestion slag powder is not greater than 3 mm.

[0013] Preferably, high-pressure spray dust suppression is used at dust-generating points during the crushing and transportation of lime digestion slag.

[0014] Preferably, in step S30, the lime digestion slag powder and coal are mixed in a certain proportion by a quantitative feeder, and the mass ratio of the lime digestion slag powder to coal is 1:(9-11).

[0015] Preferably, the temperature of the mixed coal material during combustion in the thermal power coal-fired boiler is 900°C to 950°C.

[0016] Preferably, in step S40, the particle size of the limestone powder used in the lime powder-gypsum wet method is not greater than 2 mm.

[0017] The embodiment of the present invention provides a method for recovering caustic soda from lime digester slag and desulfurizing flue gas from thermal power plants. The lime digester slag produced by preparing lime milk in an alumina production process is washed to recover caustic soda, and the lime digester slag is crushed and mixed with raw coal for flue gas desulfurization. The caustic soda from the lime digester slag can be effectively recovered and reused in desulfurization of thermal power plants, thereby reducing the caustic soda consumption of the alumina production system, reducing the cost of limestone powder flue gas desulfurization of thermal power plants coal-fired boilers, reducing the cost of external transportation of the lime digester slag and environmental protection management, and reducing the occupancy of red mud reservoirs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process diagram of the method for lime digestion slag caustic soda recovery-thermal power flue gas desulfurization in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] To make the purpose, technical solutions and advantages of the present invention clearer, the present invention is described in detail below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms, and the present invention should not be construed as being limited to the specific embodiments set forth herein. On the contrary, these embodiments are provided to explain the principles of the present invention and their practical applications, so that other persons skilled in the art can understand the various embodiments of the present invention and the various modifications suitable for specific intended applications.

[0020] An embodiment of the present invention provides a method for lime digestion slag caustic soda recovery-thermal power flue gas desulfurization, which is specifically applied in an alumina production process. The main equipment involved in the method includes a ash disintegrator, a lime milk tank, a lime milk pump, a hot water or alkali solution tank, a slag lifter, a lime slag (powder) belt, a slag washer, a hot water pipeline, a caustic soda solution pipeline, a high-humidity material two-stage crusher without a screen bottom, a lime digestion slag powder silo, a quantitative feeder and a high-pressure spray dust removal, etc., which are commonly used equipment in an alumina production process.

[0021] See also Figure 1 The process diagram of the present invention shows a method for recovering caustic soda from lime digestion residue and desulfurizing thermal power flue gas, which includes the following steps:

[0022] Step S10, using a ash dissolving machine to prepare lime milk for alumina production, wherein the produced lime digestion slag is conveyed to a slag washing machine via a slag lifting machine and a lime slag belt for washing, and the produced caustic soda overflow is recovered for preparing the lime milk.

[0023] Specifically, the lime in the lime silo is sent to the ash machine in proportion through a quantitative feeder and hot water through a hot water tank and a hot water pump (or a flat plate Al(OH)3 washing solution through an alkali liquid tank and an alkali liquid pump) to be prepared into qualified lime milk, and then sent to the downstream process of alumina production through a lime milk tank and a lime milk pump, such as the ore desulfurization blending tank area, the pre-desiliconization tank, and the comprehensive filtration process.

[0024] Specifically, the lime digestion slag produced in the preparation of lime milk is conveyed to the slag washing machine through a slag extractor and a lime slag belt to be washed with hot water, and the generated caustic soda overflow is recovered into a hot water tank or an alkali solution tank for the preparation of lime milk.

[0025] Step S20, crushing the washed lime digestion residue to obtain lime digestion residue powder.

[0026] Specifically, the washed lime digestion slag is sent to the high-humidity material non-screen bottom double-stage crusher through a chute to be crushed into lime digestion slag powder, and then transported to the lime digestion slag powder silo in the thermal power coal storage shed via a belt conveyor or a truck for storage. In the process of crushing and transporting the lime digestion slag, high-pressure spray dust suppression is used at the dust-generating points.

[0027] As a preferred solution, the particle size of the lime digestion slag powder is not greater than 3 mm.

[0028] Step S30: blend the lime digestion slag powder with coal in a certain proportion to form a mixed coal material, and send the mixed coal material into a thermal power coal-fired boiler for co-combustion to perform primary flue gas desulfurization.

[0029] Specifically, the lime digestion slag powder and coal are mixed in a certain proportion by a quantitative feeder. The mass ratio of the lime digestion slag powder to coal can be 1:(9-11), preferably 1:10.

[0030] Furthermore, the temperature of the mixed coal material in the thermal power coal-fired boiler can be 900°C to 950°C, preferably 910°C.

[0031] Step S40, the flue gas after the primary flue gas desulfurization is subjected to high-temperature dust removal and then subjected to secondary flue gas desulfurization using a lime powder-gypsum wet method.

[0032] Specifically, the flue gas after the primary flue gas desulfurization is sent to the lime powder-gypsum wet secondary flue gas desulfurization system through a high-temperature dust removal and transportation system for secondary desulfurization, and then discharged.

[0033] Preferably, the particle size of the limestone powder used in the limestone powder-gypsum wet process is not greater than 2 mm.

[0034] Based on the above process, the method provided in the embodiment of the present invention is to wash the lime digestion slag produced by preparing lime milk in the alumina production process to recover caustic soda, and then crush the lime digestion slag and burn it with raw coal for flue gas desulfurization. This can effectively realize the caustic soda recovery of the lime digestion slag and its secondary utilization in thermal power flue gas desulfurization, reduce the caustic soda consumption of the alumina production system, reduce the cost of limestone powder flue gas desulfurization of thermal power coal-fired boilers, reduce the cost of external transportation and environmental protection management of lime digestion slag, and reduce the occupancy of red mud reservoirs.

[0035] While the invention has been shown and described with reference to the particular embodiments, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the claims and their equivalents.

Claims

1. A method for recovering caustic soda from lime digestion residue and desulfurizing thermal power flue gas, characterized in that: include: S10, using a ash machine to prepare lime milk for alumina production, wherein the produced lime digestion slag is conveyed to a slag washer via a slag extractor and a lime slag belt for washing, and the produced caustic soda overflow is recovered for preparing the lime milk; S20, crushing the washed lime digestion slag to obtain lime digestion slag powder; S30, blending the lime digestion slag powder with coal in a certain proportion to form a mixed coal material, and sending the mixed coal material to a thermal power coal-fired boiler for mixed combustion to perform primary flue gas desulfurization; S40, the flue gas after the primary flue gas desulfurization is subjected to high temperature dust removal and then the secondary flue gas desulfurization is carried out by lime powder-gypsum wet method.

2. The method according to claim 1, characterized in that In step S20, the washed lime digestion slag is sent to a high-humidity material non-sieve bottom two-stage crusher through a chute to be crushed into lime digestion slag powder, and then transported to the lime digestion slag powder silo in the thermal power coal storage shed via a belt conveyor or a truck for storage.

3. The method according to claim 2, characterized in that The particle size of the lime digestion slag powder is not greater than 3 mm.

4. The method according to claim 2, characterized in that: High-pressure spray is used to suppress dust at dust-generating points during the crushing and transportation of lime digestion slag.

5. The method according to claim 1, characterized in that In the step S30, the lime digestion slag powder and coal are mixed in a certain proportion by a quantitative feeder, and the mass ratio of the lime digestion slag powder to the coal is 1: (9-11).

6. The method according to claim 5, characterized in that The temperature of the mixed coal material when burning in the thermal power coal-fired boiler is 900°C to 950°C.

7. The method according to claim 1, characterized in that In step S40, the particle size of the limestone powder used in the lime powder-gypsum wet method is not greater than 2 mm.

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