CN110358599B

CN110358599B - Agricultural and forestry waste dealkalization carbonization method based on hydrothermal reaction

Info

Publication number: CN110358599B
Application number: CN201910635273.6A
Authority: CN
Inventors: 王广伟; 王川; 张建良; 邵久刚
Original assignee: University of Science and Technology Beijing USTB
Current assignee: University of Science and Technology Beijing USTB
Priority date: 2019-07-15
Filing date: 2019-07-15
Publication date: 2021-03-23
Anticipated expiration: 2039-07-15
Also published as: CN110358599A

Abstract

The invention discloses a method for dealkalizing and carbonizing agricultural and forestry waste based on hydrothermal reaction, which comprises the steps of pretreatment of the agricultural and forestry waste, slurry preheating treatment, hydrothermal dealkalizing and carbonizing, solid-liquid separation treatment, dehydration and drying treatment, waste heat recycling and dealkalized water recycling; by controlling the raw materials and reaction conditions of the hydrothermal reaction, the agricultural and forestry waste with low utilization value and low calorific value and high alkali metal content is converted into high-quality hydrothermal carbon with high calorific value and low alkali metal content; the waste heat and the byproducts in the reaction are recycled, so that the energy consumption can be reduced, the resource utilization rate can be improved, and the environmental pollution can be reduced; the overall treatment process has high efficiency and low energy consumption, and the prepared hydrothermal carbon can be used as a high-quality clean fuel, so that the utilization value of agricultural and forestry wastes is improved, and the method has positive economic significance and ecological significance.

Description

Agricultural and forestry waste dealkalization carbonization method based on hydrothermal reaction

Technical Field

The invention relates to the technical field of utilization of agricultural and forestry wastes, in particular to a method for dealkalizing and carbonizing agricultural and forestry wastes based on hydrothermal reaction.

Background

The agricultural and forestry wastes are byproducts generated in the production and processing processes of agricultural and forestry industries, are large in quantity and various in variety, and with the rapid development of agricultural economy and the continuous progress of scientific technology, the crop yield is continuously improved, the agricultural product processing industry is also rapidly developed, so that the quantity of various agricultural and forestry wastes is continuously increased, but due to the limitation of factors such as technology, tradition and concept, the utilization rate of the agricultural and forestry wastes is still low at present. Agricultural and forestry wastes are used as renewable biomass energy sources and are burned or discarded in large quantities, so that not only is the biomass resource seriously wasted, but also the emission of greenhouse gases is increased, and the environmental pollution is aggravated. Therefore, there is a need for reasonable development and utilization of agricultural and forestry waste to improve resource utilization and reduce environmental pollution.

Currently, the main utilization mode of the agricultural and forestry wastes is carbonization quality improvement, and currently common carbonization quality improvement technologies comprise pyrolysis carbonization and hydrothermal carbonization. The pyrolysis carbonization quality improvement technology is characterized in that agricultural and forestry wastes are continuously heated under the condition of non-oxidizing atmosphere to generate a series of complex physical and chemical reactions, and partial moisture and volatile matters are removed, so that the biomass pyrolytic carbon with high calorific value and excellent powder preparation performance is obtained, but ash content in the pyrolytic biomass carbon is increased due to the fact that the ash cannot be removed in the pyrolysis process, especially the content of alkali metal is high, and therefore application of the biomass pyrolytic carbon is limited. The hydrothermal carbonization is an agricultural and forestry waste carbonization quality improvement technology which is rapidly developed in recent years, and the important difference between the hydrothermal carbonization process and the pyrolysis reaction process is that the reaction initiated by the hydrothermal carbonization process is carried out in a medium of high-temperature liquid phase water, the agricultural and forestry waste and the water are placed in a high-pressure reaction kettle to be heated, saturated steam pressure is provided by the water, the water in the agricultural and forestry waste is discharged in a liquid form, the organic macromolecular components are hydrolyzed and converted to form soluble micromolecular organic matters, meanwhile, ash in the agricultural and forestry waste can be partially removed in the hydrothermal carbonization process, and the utilization value of the agricultural and forestry waste is further improved.

The patent with publication number CN106010601A discloses a biochar prepared by using banana peel, a preparation method and application thereof, the biochar is prepared by crushing the banana peel, mixing the crushed banana peel with an aqueous solution of an activating agent, then carrying out hydrothermal carbonization reaction, washing and drying after the reaction is finished; the charcoal prepared by the method has small particle size. The characteristic of large specific surface area can be used as an adsorbent, but the heat value is low, the content of alkali metal is high, and the fuel is not suitable for use. The patent with publication number CN105602646A discloses a method for preparing biomass barbecue charcoal by hydrothermal carbonization, which adopts a process of firstly hydrothermal carbonization and then compression molding to produce clean and less-ash pure biomass barbecue charcoal; however, the method mainly focuses on improving the heat value of the carbonized product, but does not control the content of alkali metal, so that the content of alkali metal in the carbonized product is high, and meanwhile, in the hydrothermal carbonization process, the generated heat and other byproducts are not fully utilized, thereby causing certain resource waste.

Meanwhile, in the hydrothermal reaction process, due to the diversification of raw materials, preparation processes and methods, the difference of performance parameters such as ash content, volatile components, calorific value and alkali metal content of the prepared hydrothermal carbon is very large, so that the product has different performances and purposes, and diversified hydrothermal carbon products are formed.

Disclosure of Invention

The invention aims to solve the problems and provide a method for dealkalizing and carbonizing agricultural and forestry waste based on hydrothermal reaction, which converts the agricultural and forestry waste with low utilization value and high heat value and high alkali metal content into high-quality hydrothermal carbon with high heat value and low alkali metal content by controlling the raw materials and reaction conditions of the hydrothermal reaction; the waste heat and the byproducts in the reaction are recycled, so that the energy consumption can be reduced, the resource utilization rate can be improved, and the environmental pollution can be reduced; the whole treatment process has high efficiency and low energy consumption, and has positive economic significance and ecological significance.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for dealkalizing and carbonizing agricultural and forestry waste based on hydrothermal reaction comprises the following steps:

(1) pretreatment of agricultural and forestry wastes: crushing the agricultural and forestry wastes, and adding water for pulping into the crushed sample to prepare slurry;

(2) preheating the slurry: pressurizing the prepared agricultural and forestry waste slurry by a high-pressure slurry pump, and conveying the slurry to a heat exchanger for preheating;

(3) hydrothermal dealkalization and carbonization: conveying the pressurized and preheated slurry to a high-temperature high-pressure hydrothermal carbonization reaction kettle, and completing dealkalization and carbonization reactions in the reaction kettle;

(4) solid-liquid separation treatment: carrying out solid-liquid separation on the high-temperature and high-pressure materials subjected to dealkalization and carbonization treatment to obtain high-temperature hydrothermal carbon and high-temperature dealkalization water;

(5) and (3) dehydration and drying treatment: conveying the high-temperature hydrothermal carbon to a hydrothermal carbon drying system, and performing self-dehydration drying treatment by using heat energy carried by the high-temperature hydrothermal carbon to obtain hydrothermal carbon with low alkali metal content;

(6) and (3) waste heat recycling: conveying the high-temperature dealkalized water to a condensing system for cooling and depressurizing treatment, conveying the depressurized high-temperature steam to a heat exchanger, and preheating the agricultural and forestry waste slurry;

(7) and (3) recycling the dealkalized water: and (3) carrying out oil-water separation on the dealkalized water after temperature reduction and pressure reduction to obtain recyclable biomass tar and saline water.

Further, the particle size of the agricultural and forestry waste crushed in the step (1) is smaller than 1cm, the crushed agricultural and forestry waste is conveyed to a pulping tank through a pipeline, and the pulping tank is used for preparing the pulp.

Further, the pulping water in the step (1) comprises one or more of industrial water, desalted circulating water and chemical plant acid waste liquid, the pH value of the pulping water is controlled to be 2-6, and the water content of the pulp after pulping is controlled to be 60-80%.

Further, the preheating time of the preheating in the step (2) is controlled to be 20-40 min, and the preheating temperature of the slurry is 120-180 ℃.

Further, the working temperature in the hydrothermal carbonization reaction kettle in the step (3) is controlled to be 180-340 ℃, the corresponding saturated vapor pressure is 1-14.6 MPa, and the treatment time is controlled to be 20-100 min.

Further, in the hydrothermal carbon with low alkali metal content prepared in the step (5), the total mass percentage of metal potassium and sodium is less than 0.3%, and the alkali metal removal rate is more than 90%.

Further, the water content of the hydrothermal carbon with low alkali metal content prepared in the step (5) is less than 10%, the volatile content of a drying base is less than 66%, the ash content is less than 5%, the Hardgrove grindability index is more than 70, and the high calorific value is more than 20000 kJ/kg.

Further, the device adopted in the pressure reduction treatment in the step (6) is a flash tank, and high-temperature steam at 180-240 ℃ generated by pressure reduction of the flash tank is conveyed to a heat exchanger to heat the slurry.

Further, the agricultural and forestry wastes in the step (1) comprise residues of wheat, rice, corn, potatoes, oil plants, cotton, sugarcane and other crops after seeds are harvested, and non-formed trees, branches, roots, peels, fruit pits and other forestry wastes.

Further, the biomass tar in the step (7) is used as a raw material for a chemical plant; the salt-containing water is evaporated and crystallized to obtain crude sylvite which is used as a raw material by a fertilizer plant, and the residual desalted water is used as water for pulping for recycling.

The invention has the beneficial effects that:

1. the method converts the agricultural and forestry wastes with low utilization value and high heat value and alkali metal content into high-quality hydrothermal carbon with high heat value and low alkali metal content by controlling the raw materials and reaction conditions of the hydrothermal reaction; the waste heat and the byproducts in the reaction are recycled, so that the energy consumption can be reduced, the resource utilization rate can be improved, and the environmental pollution can be reduced;

2. the invention takes the agricultural and forestry waste as the main raw material, and takes the industrial water, the desalted circulating water, the acid waste liquid of the chemical plant and other aqueous solutions as the water for pulping, the raw material source is rich, the cost is low, and the waste can be fully utilized; the method comprises the steps of uniformly heating and fully contacting agricultural and forestry wastes in pulping water, and carrying out hydrothermal dealkalization carbonization reaction to prepare the hydrothermal carbon with uniform and stable performance, wherein the quality of the hydrothermal carbon can be regulated and controlled by optimizing the pH value of the pulping water, the moisture content of slurry, the hydrothermal carbonization time and the temperature, so that the performance of the prepared hydrothermal carbon meets the use requirement;

3. according to the invention, the water in the agricultural and forestry waste is discharged in a liquid state by using a hydrothermal carbonization principle, so that the heat consumed by evaporation and gasification of water vapor in the pyrolysis drying process is reduced, and the overall energy consumption is low; meanwhile, after the hydrothermal carbonization reaction is finished, solid-liquid separation and drying are firstly carried out, then cooling and depressurization are carried out, the high-temperature solid-phase hydrothermal carbon is subjected to self-dehydration drying treatment by utilizing carried physical heat, high-temperature steam generated by the decompression of the high-temperature liquid phase is used for preheating the agricultural and forestry waste slurry, and the heat utilization efficiency is high;

4. the hydrothermal carbon obtained by subjecting the agricultural and forestry waste to hydrothermal dealkalization, carbonization and quality improvement has high calorific value and low alkali metal content, and can be used as a high-quality clean fuel, so that the utilization value of the agricultural and forestry waste is improved; and the dealkalized water obtained in the reaction process can be recycled after separation, so that the comprehensive utilization rate of resources is high, the efficiency of the whole treatment process is high, the energy consumption is low, and the method has positive economic significance and ecological significance.

Drawings

FIG. 1 is a flow chart of the method for dealkalizing and carbonizing agricultural and forestry waste based on hydrothermal reaction.

Detailed Description

The present invention is further described in detail below with reference to the drawings and examples, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, and the scope of the present invention is more clearly and clearly defined. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention.

Example 1

The embodiment provides a method for dealkalizing and carbonizing agricultural and forestry waste based on hydrothermal reaction, taking corn straws as an example, and the dealkalizing and carbonizing process is shown in fig. 1, and comprises the following steps:

(1) pretreatment of agricultural and forestry wastes: crushing corn straws to enable the crushed particle size to be smaller than 1cm, conveying the crushed corn straws to a pulping tank through a pipeline, adding an aqueous solution with the pH value of 6, which is formed by mixing industrial water, desalted water and chemical plant acid waste liquid, into the crushed corn straws in the pulping tank to serve as pulping water, stirring and mixing the aqueous solution and the pulping water uniformly to obtain a pulp, and controlling the water content of the pulp to be 80%;

(2) preheating the slurry: pressurizing the prepared agricultural and forestry waste slurry by a high-pressure slurry pump, and then conveying the slurry to a heat exchanger through a pipeline for preheating, wherein the preheating time is controlled at 40min, and the preheating temperature is 120 ℃;

(3) hydrothermal dealkalization and carbonization: conveying the pressurized and preheated slurry to a high-temperature high-pressure hydrothermal carbonization reaction kettle through a pipeline, controlling the working temperature of the reaction kettle to be 180 ℃, controlling the corresponding saturated vapor pressure to be 1MPa, and controlling the treatment time to be 100min to finish dealkalization and carbonization reactions;

(4) solid-liquid separation treatment: conveying the high-temperature and high-pressure material subjected to dealkalization and carbonization treatment to a solid-liquid separation system for solid-liquid separation to obtain mud-cake-shaped high-temperature hydrothermal carbon and high-temperature dealkalized water;

(5) and (3) dehydration and drying treatment: conveying the high-temperature hydrothermal carbon to a hydrothermal carbon drying system, and carrying out self-dehydration drying treatment by utilizing physical heat carried by the high-temperature hydrothermal carbon to obtain hydrothermal carbon with low alkali metal content for use as fuel in iron and steel plants;

(6) and (3) waste heat recycling: conveying the high-temperature dealkalized water to a condensing system for cooling and depressurizing treatment, conveying 180 ℃ high-temperature steam generated by depressurizing through a flash tank to a heat exchanger through a pipeline, and preheating the agricultural and forestry waste slurry;

(7) and (3) recycling the dealkalized water: and (3) carrying out oil-water separation on the dealkalized water after cooling and depressurization to obtain recyclable biomass tar and saline water, wherein the biomass tar is used as a raw material in a chemical plant, the saline water is evaporated and crystallized to obtain crude sylvite which is used as a raw material in a fertilizer plant, and the residual dealkalized water is recycled as water for pulping.

The hydrothermal carbon with low alkali metal content prepared in the step (5) is tested, and the total mass percentage of metal potassium and sodium is 0.28%, the alkali metal removal rate is 91.6%, the water content is 9.8%, the volatile content of a drying base is 63.5%, the ash content is 4.1%, the Hardgrove grindability index is 73, and the high-grade calorific value is 21700 kJ/kg.

Examples 2 to 5

Examples 2 to 5 provide a method for dealkalizing and carbonizing agricultural and forestry waste based on a hydrothermal reaction, which is different from example 1 in that the pH value and the slurry water content of the pulping water in the step (1) are changed, and specific values of the pH value and the slurry water content of the pulping water corresponding to each example are shown in table 1:

TABLE 1 pH value and water content of pulping water corresponding to examples 2 to 5

Examples	pH value of water for pulping	Water content (%) of the slurry
			Example 2	4	80
Example 3	2	80
			Example 4	2	70
Example 5	2	60

The hydrothermal carbon prepared in each example was tested and the results are shown in table 2:

TABLE 2 Properties of the hydrothermal charcoal obtained in step (5) of examples 2 to 5

As can be seen from Table 2, the hydrothermal carbon prepared in examples 2 to 5 has an alkali metal content of 0.11 to 0.21%, a removal rate of the alkali metal of not less than 93.7%, a moisture content of 9.1 to 9.5%, a volatile content of a drying base of 64.1 to 65.6%, an ash content of not more than 4.2%, a Hardgrove grindability index of not less than 72%, a high calorific value of the drying base of not less than 21330kJ/kg, and improved performance. Wherein, comparing examples 1-3 and examples 3-5 respectively, it can be seen that the alkali metal removal rate increases with the decrease of the pH value of the pulping aqueous solution and the increase of the water content of the pulp, because the alkali metal in the biomass exists in two forms of organic and inorganic, the alkali metal inorganic salt is easily dissolved in water, and is rapidly dissolved in the liquid phase to be removed in the hydrothermal process, the decrease of the pH value of the aqueous solution increases the polarity of the solution, so that the structure of cellulose, hemicellulose and lignin in the biomass is more easily destroyed in the hydrothermal process, and the removal of the alkali metal existing in the organic form is accelerated. Therefore, during the biomass hydrothermal carbonization process, the alkali metal removal is enhanced along with the reduction of the pH value of the solution and the increase of the water content of the slurry.

Examples 6 to 13

Embodiments 6 to 13 provide a method for dealkalizing and carbonizing agricultural and forestry waste based on a hydrothermal reaction, which is different from embodiment 3 in that the working temperature, the saturated vapor pressure and the processing time in the hydrothermal carbonization reaction kettle in step (3) are changed, and specific values of the working temperature, the saturated vapor pressure and the processing time in the hydrothermal carbonization reaction kettle corresponding to each embodiment are shown in table 3:

table 3 working temperature, saturated vapor pressure and treatment time in hydrothermal carbonization reaction vessel corresponding to examples 6 to 13

The hydrothermal carbon prepared in each example was tested and the results are shown in table 4:

TABLE 4 Properties of the hydrothermal charcoal obtained in step (5) of examples 6 to 13

As can be seen from Table 4, the hydrothermal carbon prepared in examples 6 to 13 has an alkali metal content of 0.05% to 0.17%, an alkali metal removal rate of not less than 94.9%, a moisture content of 5.6% to 9.1%, a dry basis volatile matter content of 28.5% to 52.7%, an ash content of not more than 3.5%, a Hardgrove grindability index of not less than 73, a dry basis calorific value of not less than 23180kJ/kg, and improved performance.

In the comparative example 3 and the examples 6 to 9, it can be seen that the alkali metal removal rate of the prepared hydrothermal carbon is increased along with the increase of the working temperature in the hydrothermal carbonization reaction kettle in a certain range; meanwhile, as can be seen from comparison of examples 9 to 13, in a certain range, the alkali metal removal rate of the prepared hydrothermal carbon tends to increase as the hydrothermal carbonization treatment time increases; the higher the temperature and the longer the treatment time in the hydrothermal carbonization process, the more thorough the decomposition and carbonization of cellulose, hemicellulose, lignin and other substances in the agricultural and forestry waste, so that a large amount of organic functional groups are broken and decomposed, the alkali metal in an organic form is released and removed, and meanwhile, more small molecule gas is released in the biological carbonization process, the porosity is improved, a good channel is provided for the escape of the alkali metal, and the removal of the alkali metal is promoted; however, when the working temperature reaches 260 ℃ and the treatment time reaches 80min, the continuous temperature rise or the prolonged time has no obvious effect on the removal of the alkali metal, but influences the removal of the alkali metal and increases the energy consumption.

While the invention has been described with respect to specific embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes, omissions and deviations in the form and detail thereof may be made without departing from the scope of this invention; meanwhile, any equivalent changes, modifications and alterations of the above embodiments according to the spirit and techniques of the present invention are also within the scope of the present invention.

Claims

1. A maize straw dealkalization carbonization method based on hydrothermal reaction is characterized by comprising the following steps:

(1) pretreatment of corn straws: crushing the corn straws, and adding water for pulping into the crushed sample to prepare pulp; the pH value of the pulping water is controlled to be 2-6, and the water content of the pulp after pulping is controlled to be 60-80%;

(2) preheating the slurry: pressurizing the prepared corn straw slurry by a high-pressure slurry pump, and conveying the corn straw slurry to a heat exchanger for preheating;

(3) hydrothermal dealkalization and carbonization: conveying the pressurized and preheated slurry to a high-temperature high-pressure hydrothermal carbonization reaction kettle, and completing dealkalization and carbonization reactions in the reaction kettle; the working temperature of the hydrothermal carbonization reaction kettle is controlled to be 180-340 ℃, the corresponding saturated vapor pressure is 1-14.6 MPa, and the treatment time is controlled to be 20-100 min;

(6) and (3) waste heat recycling: conveying the high-temperature dealkalized water to a condensing system for cooling and depressurizing, conveying the depressurized high-temperature steam to a heat exchanger, and preheating the corn straw slurry;

2. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 1, which is characterized in that: and (2) the particle size of the crushed corn straws in the step (1) is less than 1cm, the crushed corn straws are conveyed to a pulping tank through a pipeline, and the pulping tank is used for preparing the pulp.

3. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 1, which is characterized in that: the pulping water in the step (1) comprises one or more of industrial water, desalted circulating water and chemical plant acid waste liquid.

4. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 1, which is characterized in that: the preheating time of the preheating in the step (2) is controlled to be 20-40 min, and the preheating temperature of the slurry is 120-180 ℃.

5. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 1, which is characterized in that: in the hydrothermal carbon with low alkali metal content prepared in the step (5), the total mass percentage of metal potassium and sodium is less than 0.3%, and the alkali metal removal rate is more than 90%.

6. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 5, which is characterized in that: the water content of the hydrothermal carbon with low alkali metal content is less than 10%, the volatile content of a drying base is less than 66%, the ash content is less than 5%, the Hardgrove grindability index is greater than 70, and the high calorific value is greater than 20000 kJ/kg.

7. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 1, which is characterized in that: and (4) adopting a flash tank as a device for pressure reduction treatment in the step (6), reducing the pressure of the flash tank to generate high-temperature steam of 180-240 ℃, and conveying the high-temperature steam to a heat exchanger to heat the slurry.

8. The hydrothermal reaction-based corn stalk dealkalization and carbonization method according to claim 1, which is characterized in that: the biomass tar in the step (7) is used as a raw material for a chemical plant; the salt-containing water is evaporated and crystallized to obtain crude sylvite which is used as a raw material by a fertilizer plant, and the residual desalted water is used as water for pulping for recycling.