Method for improving combustion performance of black liquor in alkali recovery furnace

Abstract

The invention relates to the technical field of black liquor combustion in alkali recovery furnaces, in particular to a method for improving the combustion performance of black liquor in an alkali recovery furnace, which comprises the following steps: adding a substance for increasing the combustion exothermic value of the black liquor and the solid concentration of the black liquor into the evaporated black liquor, mixing, and then feeding into the alkali recovery furnace for combustion; the substance for improving the burning calorific value of the black liquor and the solid concentration of the black liquor is one of coal water slurry and pulverized coal. Coal water slurry or pulverized coal is added into the evaporated black liquor, the black liquor is sent into the alkali recovery furnace for combustion after the combustion heat value and the solid matter concentration of the black liquor are increased, accordingly, the combustion heat load of the alkali recovery furnace is increased, stable combustion of the alkali recovery furnace and improvement of the steam yield are achieved, the structure is simple, operation is convenient and fast, and cost is low. The problems that the efficiency is low and the economic benefit is poor when the alkali recovery furnace combusts wheat straw pulp, bamboo pulp, chemical mechanical pulp and other pulp black liquor are effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of alkali recovery furnace black liquor combustion, and in particular to a method for improving the combustion performance of alkali recovery furnace black liquor. Background Art

[0002] Alkali recovery furnace is a device for burning papermaking and pulping black liquor and recovering steam and chemicals.

[0003] Before the black liquor is sent to the alkali recovery furnace for combustion, it needs to be evaporated and concentrated to a certain concentration. After the black liquor reaches a certain concentration and enters the furnace of the alkali recovery furnace through the spray gun, the remaining water will be completely evaporated under the high temperature environment in the furnace. After drying, the organic solids in the black liquor are thermally decomposed and carbonized, and the thermally decomposed combustible gas and carbon are burned in the furnace. As the temperature rises, the inorganic solids in the black liquor melt. Under high temperature conditions, the carbon element in the melt forms a reducing environment to cause Na2SO4 to undergo a reduction reaction to generate Na2S. After the melt enters the dissolution tank, it is sent to the next section for treatment. The flue gas generated by the combustion absorbs heat through various tube bundles and components inside the furnace to generate steam.

[0004] In order to ensure the smooth combustion and operation of the alkali recovery furnace, the black liquor concentration should generally reach more than 60% (excluding alkali ash and sodium sulfate), the calorific value of the absolutely dry black liquor solids should reach more than 3000Kcal / kg, and the operating heat load of the alkali recovery furnace should not be lower than 60%.

[0005] Compared with wood pulp black liquor, bamboo pulp and wheat straw black liquor are more difficult to increase in concentration due to their high silicon content and high viscosity. At the same time, when the concentration of wheat straw black liquor exceeds 40%, the rapid increase in black liquor viscosity makes it difficult to flow the black liquor, which affects the heat exchange efficiency of the black liquor in the evaporator and easily causes scaling of the heat exchange surface of the evaporator; the high silicon content of wheat straw black liquor also makes the heat exchange surface of the evaporator more prone to scaling; the above reasons cause wheat straw black liquor to evaporate only to a concentration of 50%, and the combustion calorific value of wheat straw black liquor is lower than that of wood pulp black liquor, which makes it difficult to stabilize the combustion of wheat straw black liquor in the alkali recovery furnace.

[0006] The black liquor of chemimechanical pulp has a lower solid content and a higher water content than chemical pulp, which results in higher evaporation costs for black liquor in chemimechanical pulping and makes it more difficult to increase the concentration.

[0007] In the alkali recovery system, since the black liquor concentration of wheat straw pulp, bamboo pulp, chemical mechanical pulp and other pulp types is difficult to increase and the calorific value of black liquor combustion is low, the alkali recovery furnaces of these pulp types are generally equipped with medium-pressure steam boilers below 3.8MPa. The lower pressure steam will affect the efficiency of the steam turbine generator, resulting in the overall economic efficiency being affected. Summary of the invention

[0008] The object of the present invention is to provide a method for improving the combustion performance of black liquor in an alkali recovery furnace.

[0009] The technical solution is as follows:

[0010] The present invention proposes a method for improving the combustion performance of black liquor in an alkali recovery furnace. A substance for improving the combustion calorific value and solid concentration of the black liquor is added to evaporated black liquor, and the mixture is then sent into the alkali recovery furnace for combustion. The substance for improving the combustion calorific value and solid concentration of the black liquor is one of water-coal slurry and coal powder.

[0011] Furthermore, the coal content in the water-coal slurry is above 65%.

[0012] Furthermore, the water-coal slurry is pumped into the inlet pipeline of the super-concentrated black liquor pump through a screw pump, and the addition ratio is controlled by a flow regulating valve; and the super-concentrated black liquor pump then transports the mixed materials to the spray gun of the alkali recovery furnace.

[0013] Furthermore, the evaporated black liquor is transported to a mixing tank through a black liquor pump, and the coal powder is added to the mixing tank at the same time; then the mixed material is pumped into a storage tank through the mixing tank pump; then the material in the storage tank is pumped into an inlet pipeline of an ultra-concentrated black liquor pump through a storage tank pump, and the addition ratio is controlled by a flow regulating valve; the ultra-concentrated black liquor pump transports the material in the storage tank to the spray gun of the alkali recovery furnace.

[0014] Compared with the prior art, the present invention adds water-coal slurry or coal powder to the evaporated black liquor to increase the combustion calorific value and solid concentration of the black liquor before sending it to the alkali recovery furnace for combustion, thereby increasing the combustion heat load of the alkali recovery furnace, achieving stable combustion of the alkali recovery furnace and increasing steam production. The present invention has a simple structure and is easy to operate, and effectively solves the problems of low efficiency and poor economic benefits when the alkali recovery furnace burns black liquor of wheat straw pulp, bamboo pulp, chemical mechanical pulp and other pulp types.

[0015] Instruction Manual

[0016] Figure 1 This is a simplified flow chart of the technical solution when adding water-coal slurry in one embodiment.

[0017] Figure 2 This is a simplified flow chart of the technical solution for adding coal powder in one embodiment.

[0018] In the figure, the super-concentrated black liquor tank contains evaporated black liquor (concentrated black liquor); using a super-concentrated black liquor pump to transport the black liquor from the super-concentrated black liquor tank to the spray gun of the alkali recovery furnace is an existing technology. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention is further described below in conjunction with specific examples. It should be understood that the following examples are only exemplary descriptions and explanations of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0020] Example 1

[0021] The evaporation station produces wheat straw dry black liquor with a solid concentration of 50%. The solid calorific value of wheat straw dry black liquor is generally around 2500Kcal / kg. According to the ratio of wheat straw dry black liquor to water-coal slurry of 1:1, 70% concentration of water-coal slurry is added and mixed to increase the solid content of the black liquor to 60% and the calorific value to around 3700Kcal / kg. The mixed black liquor is then transported to the alkali recovery furnace for combustion.

[0022] The calorific value of the mixed black liquor solids reaches or even exceeds the calorific value of most wood pulp absolute dry black liquor solids, thereby increasing the combustion heat load of the alkali furnace, achieving stable combustion of the alkali furnace and increasing steam production.

[0023] Example 2

[0024] When the evaporation section receives mixed black liquor from wood and bamboo pulp, because bamboo pulp black liquor has a higher silicon content and lower calorific value, the increase in black liquor concentration will be detrimental to the combustion of the alkali furnace. Therefore, the black liquor concentration is not easy to increase. The original evaporation production black liquor solid concentration was 72%, but the actual black liquor concentration was 67%. Figure 2 At this time, coal powder can be added into the mixing tank at a ratio of 50:9 for black liquor: coal powder, and mixed. The calorific value of the dry black liquor solids of the original bamboo and wood pulp mixed black liquor is generally around 3200Kcal / kg. The solid concentration of the black liquor after mixing with coal powder is close to 72% and the calorific value of the dry black liquor solids reaches about 3500Kcal / kg. Subsequently, the black liquor after mixing with coal powder is pumped into the storage tank by the mixing tank pump, and then pumped into the inlet pipeline of the super-concentrated black liquor pump through the storage tank pump, and the black liquor is sent to the alkali furnace for combustion through the super-concentrated black liquor pump, thereby increasing the heat load of the alkali furnace, increasing the steam production, and making the operation of the alkali furnace more stable.

[0025] Because the existing pipeline (super-concentrated black liquor pump inlet pipeline) is utilized, in order to prevent the super-concentrated black liquor pump from directly transporting the black liquor in the super-concentrated black liquor tank directly to the alkali recovery furnace, a super-concentrated black liquor outlet valve is installed at the super-concentrated black liquor pump inlet pipeline close to the interface with the super-concentrated black liquor tank, and the super-concentrated black liquor outlet valve is closed.

[0026] Example 3

[0027] The solid concentration of chemical mechanical pulp black liquor after evaporation and concentration is 60%. Using 70% concentration of water-coal slurry, chemical mechanical pulp black liquor and water-coal slurry are mixed in a ratio of 7:3. After mixing, the solid concentration is increased to 63%. The calorific value of the original chemical mechanical pulp absolute dry black liquor is about 2900Kcal / kg, and the calorific value after mixing is about 3500Kcal / kg, thereby increasing the heat load of the alkali furnace, increasing the steam production, and making the operation of the alkali furnace more stable.

[0028] Example 4

[0029] During the operation of the alkali recovery furnace, when the black liquor evaporation system does not operate normally, resulting in the concentration of the burned black liquor being lower than expected, which has an adverse effect on the combustion condition of the alkali recovery furnace, refer to Figure 1 , directly pump 70% concentration of water-coal slurry into the inlet pipeline of the super-concentrated black liquor pump through a screw pump, and the water-coal slurry and black liquor are mixed into the furnace for combustion, so that the solid content in the burning black liquor is increased, the heat load of the alkali recovery furnace is maintained within the normal range, and the impact of the low concentration of burning black liquor caused by fluctuations in the evaporation system on the normal operation of the alkali recovery furnace is reduced, the heat load of the alkali recovery furnace is increased, the steam production is increased, and the operation of the alkali recovery furnace is more stable.

[0030] Example 5

[0031] When the production system is abnormal, resulting in a low supply of dilute black liquor, which in turn leads to a low storage volume in the super-concentrated black liquor tank, making it difficult to ensure that the supply of burned black liquor meets the heat load requirement for the normal operation of the alkali recovery furnace, refer to Figure 1 , by pumping 70% concentration of water-coal slurry into the inlet pipeline of the super-concentrated black liquor pump, the water-coal slurry is mixed with the burning black liquor and entered into the furnace for combustion. The amount of water-coal slurry added is adjusted by adjusting the flow control valve to increase the heat load of the alkali recovery furnace, maintain the heat load of the alkali recovery furnace within the normal range, and reduce the impact of the low supply of dilute black liquor in the production system on the normal operation of the alkali recovery furnace in operation.

[0032] The addition points of water-coal slurry and coal powder are not limited to the positions mentioned in this specification, and the addition points of water-coal slurry and coal powder also include any addition point in the production system that can be mixed with black liquor.

[0033] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Any modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for improving the combustion performance of black liquor in an alkali recovery furnace, characterized in that: A substance for increasing the calorific value and solid concentration of the black liquor is added to the evaporated black liquor, and the mixture is then sent to the alkali recovery furnace for combustion; the substance for increasing the calorific value and solid concentration of the black liquor is one of water-coal slurry and coal powder.

2. The method for improving the combustion performance of black liquor in an alkali recovery furnace according to claim 1, characterized in that: The coal content in the water-coal slurry is above 65%.

3. The method for improving the combustion performance of black liquor in an alkali recovery furnace according to claim 1, characterized in that: The water-coal slurry is pumped into the inlet pipeline of the super-concentrated black liquor pump through a screw pump, and the addition ratio is controlled by a flow regulating valve; the super-concentrated black liquor pump then transports the mixed materials to the spray gun of the alkali recovery furnace.

4. The method for improving the combustion performance of black liquor in an alkali recovery furnace according to claim 1, characterized in that: The evaporated black liquor is transported to a mixing tank through a black liquor pump, and the coal powder is added to the mixing tank at the same time; the mixed materials are then pumped into a storage tank through a mixing tank pump; the materials in the storage tank are then pumped into an inlet pipeline of an ultra-concentrated black liquor pump through a storage tank pump, and the addition ratio is controlled by a flow regulating valve; the materials in the storage tank are transported to the spray gun of the alkali recovery furnace by the ultra-concentrated black liquor pump.

Images