METHOD FOR COMBINED THERMAL CONVERSION OF STRAW BRIQUETTE FUEL AND CARBON DIOXIDE

Description

TECHNICAL FIELD

This invention belongs to the technical field of comprehensive utilization of biomass energy and carbon dioxide, and particularly relates to a method for synergistic thermal conversion of straw briquette fuel and carbon dioxide.

BACKGROUND TECHNOLOGY

China's annual agricultural straw production is very abundant, with an annual output of 800 to 900 million tons. In addition to being partially used for papermaking and livestock feed, about 350 million tons can be used as energy, equivalent to about 180 million tons of standard coal, which is a huge number of resources. However, agricultural straw has shortcomings such as dispersed resources, low energy density, small bulk density, and inconvenient storage and transportation, which seriously restrict its large-scale application. With the increase in people's income, commodity energy (such as coal, liquefied petroleum gas, etc.) has become their main cooking energy in rural areas that are relatively close to commodity energy production areas. As a result, agricultural straw used in traditional ways can first become the object of replacement. They are discarded in the fields as organic solid waste, and some are burned at will. This not only wastes precious renewable resources, but also seriously pollutes the atmosphere and harms the human living environment. Agricultural straw briquette fuel technology can compress agricultural straw into briquette fuel with a fixed shape and high density through drying, crushing, molding and other processes, which are originally dispersed and have no certain shape, thereby saving transportation and storage costs and expanding the scope of application, improving utilization efficiency ([1] Wang Zhiwei, Lei Tingzhou, Yue Feng, Yang Shuhua, Li Zaifeng, He Xiaofeng, Zhu Jinling. Economy analysis of crop straw briquetting system. Journal of Agricultural Mechanization Research, 2012; 34 (2): 203-206. [2] Wang Zhiwei, Li Zaifeng, Lei Tingzhou, Zhu Jinling, Yang Shuhua, He Xiaofeng, Yue Zenghe. Integration and automation design of biomass briquetting fuel system. Renewable Energy Resources, 2011; 2 (4): 132-135. [3] Wang Zhiwei, Chang Xia, Lei Tingzhou, Li Zaifeng, Xin Xiaofei, Zhao Baozhu, Yang Shuhua, Yu Xianjing, Wu Yifeng, He Xiaofeng, Zhu Jinling. A briquette fuel with a flat mold molding mold. Invention patent, China, ZL2015100746651). China has released and implemented the relevant industry standards ([4] Specification for densified biofuel, NY/T 1878-2010) and local standards that have strongly promoted the promotion and application of straw briquette fuel ([5] Basic requirements for clean utilization of straw briquette fuel, DB34/T 3656-2020).

Gasification or pyrolysis of straw briquette fuel is a process that converts the hydrocarbons that make up the straw briquette fuel into combustible gases such as carbon monoxide and hydrogen under certain thermodynamic conditions. The gasification of straw briquette fuel generally uses gases such as nitrogen, argon, helium, air, water vapor, or a mixture of these gases to convert the agricultural straw briquette fuel into combustible gases such as carbon monoxide, hydrogen, and methane through thermochemical reactions ([6] Zhang Weijie, Guan Haibin, Jiang Jianguo, Sun Rongfeng, Fan Xiaoxu, Yang Liguo, Liu Zuo, Hu Safe. Gasification experiment of straw briquette fuel in a compound fixed bed. Shandong Science. 2017; 30 (4): 67-72). The pyrolysis of the straw briquette fuel is generally heated under the condition of separation of the gas to transform straw briquette fuel into low-molecular combustible gas ([7] Wang Zhiwei, He Xiaofeng, Zhao Baozhu, Bai Wei, Zhu Jinling, Lei Tingzhou. Experimental study of utilization system on biomass pyrolysis. Journal of Agricultural Mechanization Research, 2009; 31 (3): 150-153).

Straw briquette fuel is different from fossil fuels such as coal. It contains hydrocarbons and also contains more oxygen. Therefore, when heating straw briquette fuel at high temperature, the oxygen-containing bond is broken and gases containing carbon dioxide is generated. After the pyrolysis continues for a certain period of time, the oxygen element is exhausted. At this time, the volatile component can be further cracking under the conditions of air, oxygen, water vapor and other atmosphere gas ([8] Wang Shurong, Luo Zhongzheng. Pyrolysis of biomass components. Beijing: Science Press, 2013). In addition, adding catalysts can promote further deep cracking reactions of volatile component and hydrocarbons during biomass thermal conversion, and generate combustible gas with a smaller molecular weight, thereby reducing the generation of tar, increasing gasification efficiency of straw briquette fuel, increasing heat value of combustible gas, and increasing energy conversion rate.

The efficient and reasonable use of carbon dioxide is an important strategy to reduce the greenhouse gas and achieve carbon neutrality. In the process of pyrolysis and thermal conversion of straw briquette fuel, volatile component contains the long chain hydrocarbons, which in turn causes tar and becomes the main factor that hinders the efficient utilization of straw briquette fuel. However, there is no public reports on the method of coordinating thermal conversion of straw briquette fuel and carbon dioxide under the action of catalysts.

Invention Content

This invention uses straw briquette fuel and carbon dioxide as raw materials. Under the action of the nickel-based catalyst, the straw briquette fuel and carbon dioxide are converted into high-quality combustible gas. This invention divides the pyrolysis and gasification of straw briquette fuel into multiple stages through the process of supplying carbon dioxide, ensuring the coordinated conversion of carbon dioxide and straw briquette fuel, and generating more combustible gas such as carbon dioxide, hydrogen and short-chain-based hydrocarbon combustible gas. In addition, the method of combining carbon dioxide with the catalyst promotes efficient utilization of the catalyst, and at the same time avoids the catalyst being covered, carbon deposition and ash deposition during the thermal conversion, greatly extending catalyst lifetime and reducing operating costs.

This invention provides a method for synergistic thermal conversion of straw briquette fuel and carbon dioxide, which realizes synergistic thermal conversion of straw briquette fuel and carbon dioxide, generates high-quality combustible gas while consuming and fixing carbon dioxide.

The raw materials used in this invention are straw briquette fuel and carbon dioxide. Under a fixed reaction temperature and a reasonable ratio of catalyst to straw briquette fuel, by controlling the input flow rate of carbon dioxide with the reaction time, the reasonable cracking and gasification reaction of the straw briquette fuel and carbon dioxide is achieved, thereby generating high-quality syngas and at the same time fixing carbon dioxide. The process method of this invention is simple, the gas product does not need to be separated, and the carbon and ash deposits on the catalyst are avoided. The obtained combustible gas has high heating value and high hydrogen content. The implementation of this invention patent is conducive to the large-scale treatment and energy utilization of organic solid waste such as straw, and accelerates the realization of the goal of carbon neutrality.

Preferably, 1 unit weight of nickel-based catalyst is placed in the gasification furnace, and after the reaction temperature is stabilized, straw briquette fuel 1 to 3 times the mass of the catalyst is placed, that is, the original mass ratio of straw briquette fuel and nickel-based catalyst is about 3:1 to 1:1.

Preferably, the temperature in the gasification furnace is maintained at 810-960° C., and the reaction time is set to 60 minutes. According to different reaction temperatures, no carbon dioxide is introduced in 0 to 10 minutes, the carbon dioxide introduced into the gasifier is 0.016 to 0.04 unit weight/min from 5 to 10 min, and the carbon dioxide introduced into the gasifier is 0.012 to 0.03 unit weight/min from 14 to 60 min. The gas in the gasifier is extracted to the gas storage device through a Roots blower.

Preferably, after 60 minutes of the first reaction, the slag after the reaction is removed or filtered, and the straw briquette fuel is re-added 1 to 3 times the weight of the catalyst. The steps for introducing the amount of carbon dioxide are the same as the first reaction of 60 minutes, and the subsequent reaction cycle is carried out to achieve synergistic thermal conversion of straw briquette fuel and carbon dioxide, generating high-quality combustible gas while fixing carbon dioxide.

The mechanism of this invention is: at a certain temperature, the initial cracking of the straw briquette fuel will produce a certain amount of carbon dioxide, the volatile component generated after cracking for a certain period of time reacts with the carbon dioxide to generate a certain number of combustible gases such as carbon monoxide, hydrogen and long-chain hydrocarbons. Then the long-chain hydrocarbon components undergo deep catalytic cracking under the action of the nickel-based catalyst, generating more hydrogen and short-chain hydrocarbons and other gases, thereby improving the gasification efficiency of the straw briquette fuel and the fixed utilization of carbon dioxide.

This invention uses straw briquette fuel and carbon dioxide as raw materials, and converts the straw briquette fuel and carbon dioxide into high-quality combustible gas under the joint action of a nickel-based catalyst. Compared with existing reports, the advantage of this invention is that the nickel-based catalyst used has low cost and high catalytic activity. At the same time, combined with the participation of carbon dioxide, the nickel-based catalyst is prevented from being covered, carbon deposited and dust deposited, greatly extending the life of the catalyst and reducing operating costs; Under reasonable time planning conditions, carbon dioxide can fully react with the cracked gas of the straw briquette fuel, fixing the carbon dioxide and producing more combustible gas. However, in the existing technology, there is no catalytic synergistic thermal conversion method using straw briquette fuel and carbon dioxide.

DETAILED IMPLEMENTATION

The technical solutions of this invention are described below with specific examples, but the protection scope of this invention is not limited thereto:

The reaction temperatures selected in Examples 1 to 4 are 810° C., 860° C., 910° C., and 960° C. respectively, and the selected straw briquette fuel are cornstraw briquette fuel.

Example 1

Put a unit weight (such as 100 kg) of nickel-based catalyst (Ni/Al₂O₃) in the biomass gasifier, keep the temperature inside the gasifier at 810° C., and add corn straw briquette fuel that is twice the weight of the catalyst (such as 200 kg). Set the reaction time to 60 min, in which no carbon dioxide is introduced from 0 to 10 min, the carbon dioxide introduced into the gasifier from 11 to 20 min is 0.016 unit weight/min, and the carbon dioxide introduced into the gasifier from 21 to 60 min is 0.012 unit weight/min. The gas in the gasifier body is extracted to the gas storage device through a Roots blower. After 60 min, remove or filter the slag after the reaction, and re-add corn straw briquette fuel 1 to 3 times the weight of the catalyst. Start timing and proceed according to the above carbon dioxide flow rate and time until 60 minutes. The above steps are carried out in a loop.

Example 2

Put a unit weight (such as 100 kg) of nickel-based catalyst (Ni/Al₂O₃) in the biomass gasifier, keep the temperature inside the gasifier at 860° C., and add corn straw briquette fuel that is twice the weight of the catalyst (such as 200 kg). Set the reaction time to 60 minutes, in which no carbon dioxide is introduced from 0 to 8 min, the carbon dioxide introduced into the gasifier body from 9 to 18 min is 0.022 unit weight/min, and the carbon dioxide introduced into the gasifier body from 19 to 60 min is 0.017 unit weight/min. The gas in the gasifier body is extracted to the gas storage device through a Roots blower. After 60 min, remove or filter the slag after the reaction, and re-add corn straw briquette fuel 1 to 3 times the weight of the catalyst. Start timing and proceed according to the above carbon dioxide flow rate and time until 60 minutes. The above steps are carried out in a loop.

Example 3

Put a unit weight (such as 100 kg) of nickel-based catalyst (Ni/Al₂O₃) in the biomass gasifier, keep the temperature inside the gasifier at 910° C., and add corn straw briquette fuel that is twice the weight of the catalyst (such as 200 kg). Set the reaction time to 60 minutes, in which no carbon dioxide is introduced from 0 to 6 min, the carbon dioxide introduced into the gasifier body from 7 to 16 min is 0.031 unit weight/min, and the carbon dioxide introduced into the gasifier body from 17 to 60 min is 0.023 unit weight/min. The gas in the gasifier body is extracted to the gas storage device through a Roots blower. After 60 min, remove or filter the slag after the reaction, and re-add corn straw briquette fuel 1 to 3 times the weight of the catalyst. Start timing and proceed according to the above carbon dioxide flow rate and time until 60 minutes. The above steps are carried out in a loop.

Example 4

Put a unit weight (such as 100 kg) of nickel-based catalyst (Ni/Al₂O₃) in the biomass gasifier, keep the temperature inside the gasifier at 960° C., and add corn straw briquette fuel that is twice the weight of the catalyst (such as 200 kg). Set the reaction time to 60 minutes, in which no carbon dioxide is introduced from 0 to 4 min, the carbon dioxide introduced into the gasifier body from 5 to 13 min is 0.040 unit weight/min, and the carbon dioxide introduced into the gasifier body from 14 to 60 min is 0.030 unit weight/min. The gas in the gasifier body is extracted to the gas storage device through a Roots blower. After 60 min, remove or filter the slag after the reaction, and re-add corn straw briquette fuel 1 to 3 times the weight of the catalyst. Start timing and proceed according to the above carbon dioxide flow rate and time until 60 minutes. The above steps are carried out in a loop.

Table 1 shows the amount of combustible gas components generated and carbon dioxide consumption within a reaction time of 60 minutes in Examples 1 to 4:

It can be seen from Table 1 that under the conditions of 810° C., 860° C., 910° C., and 960° C., 1 unit weight of corn straw briquette fuel can produce approximately 0.68 to 1.83 unit weight of carbon monoxide, about 0.011 to 0.030 unit weight of hydrogen, about 0.069 to 0.072 unit weight of methane, and about 0.032 to 0.041 unit weight of low carbon chain hydrocarbon gas. At the same time, it can consume approximately 0.29 to 1.27 unit weigh of carbon dioxide.