CN112555870B

CN112555870B - Straw gasification combustion-heat energy grain drying coupling technology for heavy metal pollution farmland restoration

Info

Publication number: CN112555870B
Application number: CN202011134497.8A
Authority: CN
Inventors: 杨肖娥; 潘明辉; 梁尹明; 盛奎川
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2020-10-21
Filing date: 2020-10-21
Publication date: 2022-09-27
Anticipated expiration: 2040-10-21
Also published as: CN112555870A

Abstract

The invention discloses a straw gasification combustion-heat energy grain drying coupling technology for restoring a heavy metal polluted farmland, belonging to the technical field of biomass heat conversion, and the method comprises the following steps: (1) selecting to establish a straw gasification combustion furnace coupled with a grain drying base near the plant restoration project; (2) mechanically packaging the rice straws subjected to phytoremediation on site, and transporting the rice straws to a grain drying base; (3) directly feeding the straw bag into a gasification combustion furnace, gasifying the straw bag in a gasification chamber, and enabling the generated combustible gas to enter a combustion chamber for full combustion to generate hot flue gas; (4) the hot flue gas and the external air are subjected to heat exchange in the heat exchanger to heat the external air to form clean hot air, and the hot air is sent into the grain dryer through a pipeline to dry the grains. The method of the invention realizes mechanization completely, and can save the cost of farmers for drying the paddy; the flue gas after gasification and combustion is discharged after dust removal treatment, and the carbon ash is recycled uniformly, so that the problem of secondary pollution of the rice straw polluted by heavy metal is solved.

Description

Straw gasification combustion-heat energy grain drying coupling technology for heavy metal pollution farmland restoration

Technical Field

The invention relates to the technical field of post-treatment of heavy metal polluted farmland phytoremediation straws and biomass heat energy conversion and utilization, in particular to an integrated technical method for mechanical packing, whole-package pyrolysis and gasification combustion and heat energy drying of heavy metal polluted farmland crop straws.

Background

At present, the heavy metal pollution situation of soil in China is severe. Heavy metals are different from other organic pollutants, have non-biodegradability, can exist in soil for a long time, and can be accumulated in human bodies and animal bodies through food chains after being absorbed and enriched by plants and other organisms due to high toxicity and biological enrichment property, so that serious damage is caused to the safety of ecological systems and food, and the human health is finally endangered.

In recent years, a phytoremediation technology is taken as an in-situ efficient and environment-friendly remediation technology, and can be carried out in a mode of production and remediation at the same time in actual remediation engineering, for example, patent documents CN109530417A and CN110238175B disclose that rape-medium rice wheel is utilized to carry out remediation and production at the same time on Cd in farmland soil, and the technology is low in cost, simple to operate, accepted by wide grain farmers and has strong popularity. The plant restoration technical mode of production and restoration can generate a large amount of crop straws with heavy metal and low pollution every year, if the crop straws are directly returned to the field or burnt on the spot, the secondary pollution can be caused to the environment, the restoration efficiency of plant restoration can be reduced, and therefore, after the crops in the heavy metal polluted farmland are harvested, the residual straws must be removed.

At present, the energy regeneration/resource utilization of biomass can be realized through the thermochemical conversion technologies such as gasification, pyrolysis carbonization and incineration. However, the method is limited by the conditions that the heat value of the paddy straw in the heavy metal polluted farmland is not high, the contents of ash, moisture and heavy metal are more, the stacking density is low, the transportation cost is high, and the like, and the technologies are directly used for repairing the crop straw, so that the method has low benefit, high energy consumption, secondary pollution to the environment and incapability of realizing industrialization.

Meanwhile, the agricultural products are dried every year, a large amount of fossil energy is consumed, and the consumption of the energy not only increases the economic burden of farmers, but also causes certain pollution to the environment.

Therefore, how to effectively treat crop straws lightly polluted by heavy metals after phytoremediation, avoid secondary pollution to the environment, improve the phytoremediation efficiency and the economic benefit of phytoremediation, and realize sustainable development of phytoremediation is a problem to be solved by technical personnel in the field.

Disclosure of Invention

The invention aims to provide an integrated treatment technology of mechanical packaging of heavy metal polluted rice straws, complete package gasification combustion and heat energy drying of rice after plant restoration, which not only avoids secondary pollution of the heavy metal polluted rice straws to the environment, but also can fully utilize the residual value of the straws.

In order to realize the purpose, the invention adopts the following technical scheme:

a straw gasification combustion-heat energy grain drying coupling technology for restoring heavy metal polluted farmland comprises the following steps:

(1) establishing a straw gasification combustion furnace coupled grain drying base near the heavy metal polluted farmland production and repair engineering;

(2) the straw after heavy metal restoration rice harvesting in the farmland is mechanically packed on site and transported to a straw gasification combustion furnace coupled grain drying base;

(3) directly feeding the straw bag into a gasification combustion furnace, gasifying the straw bag in a gasification chamber, and feeding the generated combustible gas into a combustion chamber along with a pipeline for full combustion to generate hot flue gas;

(4) the hot flue gas exchanges heat with external air sucked by a fan in a heat exchanger to heat the external air to form clean hot air, and the hot air is sent into a grain dryer through a pipeline to dry grains; the flue gas after heat exchange is subjected to dust removal treatment to reach the emission standard of atmospheric pollutants of the boiler and then is discharged;

and (4) recycling carbon ash generated after the straw is combusted as hazardous waste solids for harmless treatment.

According to the invention, the grain dryer is powered by gasifying and burning the heavy metal polluted rice straws, in the step (1), a straw gasification combustion furnace is arranged near a production and repair project for every 100-1000 mu of heavy metal polluted farmland, and is coupled with a grain drying base, so that the harvested grains are subjected to centralized drying treatment, the current-season rice is dried by using the current-season straws, the convenience and the rapidness are realized, the production cost is greatly saved, and the actual drying cost can be saved by more than 30%.

Furthermore, the straw gasification combustion furnace is coupled with a grain drying base and is arranged within a range of 5 kilometers from the heavy metal polluted farmland production and remediation project.

Specifically, a gasification heat energy utilization system is established in a raw grain drying base, the system consists of a straw gasification combustion furnace and a grain dryer, and the straw gasification combustion furnace and the grain dryer are connected through a heat exchanger. The gasification combustion furnace and the grain dryer can both adopt the existing equipment, and are provided with the gasification combustion furnace and the dryer with corresponding quantity according to the actual grain drying requirement.

The gasification combustion furnace is provided with water mist/plasma/cloth bag dust removal equipment and an electric conveyor belt, preferably, the gasification combustion furnace is an improved fixed chain grate furnace bridge combustor, and the whole system is provided with a variable frequency motor, a control speed regulator, an electric conveyor belt and a cloth bag dust remover.

In the step (2), the rice straw subjected to phytoremediation is packaged on site by a straw packaging machine after the rice is harvested, the straw volume can be greatly reduced by mechanical packaging, stacking and transportation are facilitated, and the nearby transportation cost is lower.

Furthermore, the harvested rice straws are naturally aired in the farmland for 2-3 days, and the water content of the straws is controlled within 30%.

And packaging the aired rice straws into straw bags with the cross section size of 30-40 cm multiplied by 40-50 cm and the length of 30-70 cm. The straw bag with the size is convenient to stack and transport, and can ensure that the straw inside is fully gasified during combustion.

In the step (3), the straw bags conveyed to the grain drying base are directly fed into a gasification combustion furnace for gasification without being crushed to generate biomass carbon, heavy metals are enriched on the biomass carbon and generate a large amount of combustible gas, and the combustible gas enters a combustion chamber through a pipeline for full combustion and is converted into hot flue gas.

Furthermore, the straw bags are fed intermittently through the electric conveyor belt, and the whole process is mechanically operated. Preferably, the feeding interval time is 480-780 seconds.

Heavy metal pollution in farmland is mainly cadmium, so that a large amount of cadmium is prevented from volatilizing, and meanwhile, the straw gasification is sufficient, and the gasification temperature is controlled within 1000 ℃. Preferably, the gasification temperature is 700-1000 ℃. More preferably, the gasification temperature is 800-900 ℃.

Furthermore, combustible gas generated by gasification enters the combustion chamber for full combustion, and a plurality of secondary air inlets are formed in the combustion chamber.

And (4) recovering and treating the carbon ash generated after combustion. Heavy metals in the rice straws are retained in the carbon ash, and the carbon ash can not return to farmlands and needs to be recycled uniformly. And can be used as an environment-friendly material for adsorption and catalysis of water gas pollutants.

Because ash content moisture is all more in the straw, the dust is more in the hot flue gas of production, can't directly be used for grain to dry, need obtain clean hot-blast through heat exchange heating outside air, utilizes clean hot-blast drying grain. Specifically, the axial flow fan sucks external clean air into the heat exchanger to perform heat exchange at a flow rate of not less than 10 m/s. The obtained clean hot air is sent into the dryer through the air supply device.

Furthermore, the automatic control device is used for regulating and controlling the temperature of hot air sent into the grain dryer, so that the grain dryer meets the grain drying requirement.

Furthermore, clean hot air is delivered into the grain dryer through an air delivery pipeline with a heat insulation device, so that heat loss in the pipeline is reduced.

In order to meet the emission standard, the flue gas after heat exchange needs to be subjected to dust removal treatment, and the dust removal treatment can be water mist, cloth bag or plasma dust removal. Preferably, a bag-type dust collector is arranged on the heat exchanger.

The invention has the following beneficial effects:

(1) according to the integrated treatment method provided by the invention, all links of straw packing, straw feeding, straw gasification combustion and grain drying are mechanized, so that the cost of rice drying by farmers can be saved, and the atmospheric pollution caused by large-area straw combustion can be reduced; the flue gas after gasification and combustion is discharged after dust removal treatment, and the carbon ash is recycled uniformly, so that the problem of secondary pollution of rice straws polluted by heavy metal is solved.

(2) The method optimizes the treatment process of the rice straws polluted by heavy metals after phytoremediation, avoids secondary pollution of the rice straws polluted by the heavy metals to the environment, utilizes the residual value of the straws, indirectly reduces the application of nitrogen fertilizer to farmlands, adjusts the carbon-nitrogen ratio of the farmlands, improves the remediation efficiency of the phytoremediation technology of the farmlands polluted by the heavy metals, and has extremely high feasibility and economical efficiency.

Drawings

FIG. 1 is a flow chart of straw treatment in example 1.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1

Test site: the heavy metal polluted farmland of a certain Cd in a thoroughfare and thoroughfare area in Zhejiang province is produced and repaired at the same time.

The area of the demonstration area is 100 mu, the average Cd pollution concentration is 0.76ppm, the soil PH (1: 2.5) is 4.69, and the average Cd pollution concentration in the rice straw is 0.34 ppm.

Establishing a gasification heat energy utilization system: a gasification combustion furnace produced by Zhejiang warm heat energy science and technology Limited company and a bag-type dust collector and an electric conveyor belt which are matched with the gasification combustion furnace are built in a grain drying base, and then are connected with four grain drying machines through matched heat converters. The system is assembled from existing equipment.

Mechanically baling rice straw on site: the distance between a farmland and a drying base in a restoration demonstration area is about 3 kilometers, restored rice straws are harvested in a single season, the rice straws are aired in the farmland for 2 days and then packaged by a straw packaging machine, specifically, a 9YFL-1.9 type crawler self-propelled square bale bundling machine produced by starlight agricultural machinery company Limited is adopted to package the rice straws into straw packages with the length, width and height of 36cm multiplied by 46cm multiplied by 50cm, and then the straw packages are transported to a grain drying base in batches.

Straw bag gasification combustion: the straw bags are not required to be crushed, and directly enter a gasification combustion furnace in an intermittent feeding mode through an electric conveyor belt, the interval time is 580 seconds, the gasification is carried out, and the temperature in the gasification furnace is controlled at 800 ℃; then the generated combustible gas enters the combustion chamber together for full combustion to generate hot flue gas.

Drying agricultural products: hot flue gas generated by gasification combustion of straw bags is subjected to heat exchange with external air through a heat exchanger, the external air is heated and converted into clean hot air, the hot air is sent into a rice dryer through a hot air pipe with a heat insulation measure, grains are dried, and 17.14 bags of straw are averagely needed for drying each ton of grains.

The above operation flow is shown in fig. 1. Through calculation, compared with the method that farmers use biomass granular fuel to dry rice, the cost is reduced by 40%.

And the flue gas after heat exchange is dedusted by water mist and discharged after reaching the atmospheric pollutant emission standard of the GB 13271-2014 boiler. The smoke test reports for emissions are shown in table 1.

TABLE 1

Carbon ash generated by gasification and combustion of the rice straw polluted by heavy metal is recycled uniformly and treated harmlessly.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A straw gasification combustion-heat energy grain drying coupling method for heavy metal pollution farmland restoration is characterized by comprising the following steps:

(1) the method comprises the following steps of establishing a straw gasification combustion furnace coupled grain drying base within 5 kilometers of a heavy metal polluted farmland production and restoration project every 100-1000 mu, and establishing a gasification heat energy utilization system in the base, wherein the system consists of the straw gasification combustion furnace and a grain dryer, and the straw gasification combustion furnace and the grain dryer are connected through a heat exchanger;

(2) naturally airing the harvested straws of the heavy metal restoration paddy in the farmland, controlling the water content of the straws to be within 30%, mechanically packaging the straws into straw bags with the cross-sectional dimension of 30-40 cm multiplied by 40-50 cm and the length of 30-70 cm on site, and conveying the straw bags to a straw gasification combustion furnace coupled grain drying base;

(3) directly feeding straw bags into a gasification combustion furnace, intermittently feeding through an electric conveyor belt, setting the feeding interval time to be 480-780 seconds, gasifying in a gasification chamber at the temperature of 800 ℃ to generate biomass carbon, enriching heavy metals on the biomass carbon, and allowing generated combustible gas to enter the combustion chamber along with a pipeline for full combustion to generate hot flue gas;

(4) the hot flue gas exchanges heat with external air sucked by a fan in a heat exchanger, the fan sucks external clean air into the heat exchanger, the heat exchange is carried out at the flow speed of not less than 10m/s, the external air is heated to form clean hot air, the hot air is sent into a grain dryer through a pipeline to dry grains, and the temperature of the hot air sent into the grain dryer is regulated and controlled by an automatic control device; the flue gas after heat exchange is subjected to dust removal treatment, wherein the dust removal treatment is water mist, cloth bag or plasma dust removal, and the flue gas is discharged after reaching the emission standard of atmospheric pollutants of a boiler;

and (3) bagging and recycling carbon ash generated after the straw is combusted as hazardous waste solids for harmless treatment.