Study on Slurry Forming Properties of Coal/Modified Biomass Blending Pulping

Abstract

Rice straw is an agricultural waste that is usually utilized by direct burning or landfilled which pollutes the environment. Crushing and blending into coal water slurry can effectively utilize the calorific value of rice straw and protect the environment. Due to its characteristics of strong water absorption, poor grindability, and many pores, it is not conducive for the preparation of good slurry. This paper uses temperature modification to evaluate the slurry performance of the biomass coal water slurry prepared by mixing rice straw and coal powder. The research, comparative analysis of the difference in the pulping performance of the slurry prepared by mixing rice straw before and after the modification, and the effect of the modification temperature and the modification time on the pulping performance of the slurry are summarized. The experimental results show that: the rheological index (n) of the slurry made from unmodified rice straw is the smallest, and the smallest n=0.21. Modification at different temperatures increases the rheological index of the slurry. Modification at 105?and 200?did not improve the slurry formation performance. Modification at 250?and 350?both increased the slurry concentration of 3g and 5g rice mixture by 3% and 2%, respectively. Moreover, the fluidity of the slurry was B, and the results of rod drop experiment showed that the water separation rate was small and the slurry was soft precipitation. Therefore, the modification effect at 250?and 350?is better.

Introduction

I. INTRODUCTION

With the development of the global economy and the continuous advancement of the industrialization process, the people's living standards have been improved, and the demand for various types of energy has also been increasing. In today's energy structure in the world, oil, coal and natural gas firmly occupy the top three positions [1]. They account for 85% of the primary energy structure and are today's main energy sources. However, in the future, as energy demand continues to change, major global energy structures will also undergo major adjustments. The overall trend can be summarized as: low-carbon and renewable. From an environmental point of view, if petrochemical resources are not used cleanly, it will inevitably aggravate the "greenhouse effect" and increase the emission of polluting gases and the accumulation of solid waste, which will damage the global ecological environment. Therefore, finding environmentally clean yet efficient ways of Utilizing its Vast Energy resources has been an important issue in the direction of environmental protection in China,

In China’s primary energy consumption structure, coal occupies a dominant position. According to the 2019 China Statistical Yearbook of the National Bureau of Statistics, as of the end of 2019 [2], Chinas total energy consumption (unit: standard coal) was 4.86 billion tons of standard coal, of which the total annual coal consumption in the past 8 years (unit: Standard coal) reached more than 2.7 billion tons. Therefore, it is not difficult to see that coal will still dominate energy consumption for a long time to come. However, with the development of technologies such as coal conversion and utilization, because coal contains many harmful elements and pollutants, the "greenhouse effect" caused by coal combustion has increased and the harmful gases in the atmosphere have increased [3]. Some scholars predict [4] that if the current situation is developed and no measures are taken to control it, it is estimated that by 2030, China's CO2 emissions caused by coal burning will reach about 9.2 billion tons. In this context, clean coal technology has become an important way to control coal pollution.

Biomass, among all the renewable and carbonaceous resources, is considered as a carbon neutral energy [5]. The use of biomass is favorable for reduction of CO2 emission, and as well as NOx [6]and SO2 emissions [7]. However, biomass presents lower energy density and higher transportation cost and it needs to be upgraded before utilization. It is reported that China's total biomass energy is about 1 billion tons of standard coal, including forestry and agricultural residues, domestic waste, domestic sludge and human and animal manure. The results of the Ninth National Forest Resources Inventory [8] that the forest area in China is 2.2× 10 8 hm 2 , of which the annual output of the remaining biomass resources from forest tending and timber harvesting is about 1.95 × 10 8 t. China is rich in straw biomass resources.

According to the data [9], in 2017, the theoretical production of straw in China is about 10 × 10 8 t , the amount of straw collectible resources is about 9 × 10 8 t , and the utilization of straw is about 7.2 × 10 8 t. t . According to statistics [10], domestic waste treatment volume in 2017 was 3.39 × 108 t , including 2.26 × 108 t for landfill , 0.93 × 108 t for incineration, and 0.20 × 10 t for other treatment . 8 t; In 2017, the production volume of dry sludge was 10.2671 million tons, and the disposal volume was 10.059 million tons. The countries with better development of the biomass energy industry includes the United States, Germany and Japan, etc., focusing on the development of industries such as biomass fuel and biomass power generation. It is estimated that by 2035, biomass fuels will replace about half of the traditional energy in the world [11]. In order to effectively utilize biomass energy, the selection of biomass treatment methods is very important. The treatment methods mainly include biological methods, physical methods, chemical methods, and combined physical and chemical methods. The treatment method has advantages and disadvantages. Although biomass energy can be effectively utilized, there may be disadvantages such as high treatment cost, high energy consumption, and the generation of harmful substances during the treatment. For example, the commonly used mechanical pulverization treatment method of straw can be used more effectively after treatment. The advantages of this method are simple operation and easy implementation, but there are disadvantages such as large energy consumption and limited pulverization particle size [12]. At present, the more commonly used biomass disposal methods such as landfill, incineration, biogas production, etc., although landfill and incineration methods can quickly process a large amount of biomass and the treatment cost is low, but there are low biomass utilization rates, serious environmental pollution, etc. The problem is that biogas-based is relatively more environmentally friendly, with higher biomass utilization and better economic benefits. The existing biomass utilization technology has many shortcomings, so in recent years, many scholars have studied the blending of biomass and coal powder to prepare biomass coal-water slurry. Coal-water slurry is a new type of coal -based liquid fuel that emerged in the 1970s. The coal -water slurry production process (equipment) will develop toward cleanliness, high efficiency, and low energy consumption, and the choice of coal for pulping will develop toward low-cost coal, coal blending, and industrial and domestic waste. Based on the important role of fuel coal-water slurry in energy saving and emission reduction, it has broad development prospects in the fields of fuel substitution for oil, burning in urban (heating) furnaces, and gas coal-water slurry gasification.  In recent years, there have been many studies on other biomass CWS. Biomass such as straw, medicinal residues, aquatic organisms, etc. are mixed with coal powder to obtain biomass CWS. At present, there are some studies on the preparation of straw coal slurry by blending wheat straw with coal. Zang Zhuoyi et al. [13] used low-temperature carbonization to treat wheat straw, studied the pulping properties of the slurry prepared before and after carbonization, and investigated the effects of carbonization temperature and wheat straw addition on the pulp properties, the results showed that the more wheat straw, the poorer the pulpability and fluidity of the pulp, but the stability was improved. With the increase of carbonization temperature, the pulpability of the pulp was gradually improved. Li Tingting [14] studied the preparation of wheat straw-coal water slurry and its pulping characteristics, still using low-temperature carbonization, and compared the differences in the pulping characteristics before and after carbonization. Carbonization treatment improves its grindability and improves the pulping performance of wheat straw-coal slurry. Li Xiang [15] used coal tar and diesel oil to modify straw to prepare modified straw coal - water slurry. Zhou Zhijun et al. [16] used drying to treat waste rice straw and then ground it into powder, which was mixed with pulverized coal in a certain proportion to prepare biomass coal-water slurry. Wang et al. [17] prepared coal slurry fuel by mixing pharmaceutical fermentation residue with pulverized coal, water and dispersant, and explored the effect of pharmaceutical fermentation residue on the slurry -forming properties of the slurry. The study showed that the slurry showed strong shear thinning. Characteristic and has high apparent viscosity, pharmaceutical fermentation residue can reduce the solid-liquid separation of coal-water slurry, thereby improving the stability of coal-water slurry. Zhang Ye et al. [18] studied the pulping characteristics of bacterial residue coal slurry, and the results showed that bacterial residue can be used as a stabilizer for CWS. Liu et al. [19] studied the Rheological behavior and stability characteristics of biochar-water slurry fuels, emphasis on the Effect of biochar particle size and size distribution. This topic mainly studies the preparation of biomass coal-water slurry by blending modified biomass and pulverized coal, and examines the slurry -forming properties of the slurry. It can not only effectively utilize the waste biomass, but also prepare a coal-water slurry with excellent slurry-forming properties. In this paper, Huainan XQ coal and rice straw were selected, and industrial analysis and ash component analysis were carried out on these two raw materials. The particle size analysis of XQ coal was further carried out to investigate the properties of raw coal and biomass characteristics. Three kinds of additives were used to prepare CWS, to select the most suitable; then we prepared biomass CWS and modified biomass CWS, and the modification method adopted was temperature modification. Furthermore, we studied the slurrying properties of biomass CWS and modified biomass CWS, comparative analysis of the differences in the slurry properties of biomass CWS before and after modification, and further investigation of the effect of modification temperature and biomass blending amount was carried. The effect of slurry forming properties.

II. EXPERIMENTAL

A. Materials

China Huainan, XQ coal and rice straw were selected, and industrial analysis analyzed according to GB/T212-2008 and GB/T213-2008 seen in Table II, and ash component analysis were carried out on these two raw materials. Coal and char samples were dried and grounded to similar particle size distributions for satisfying the requirements of slurry fuels. The particle size analysis of XQ coal was further carried out to investigate the properties of raw coal and biomass characteristics Using the BT-9300ST laser particle size distribution analyzer Fig 1-2 and Table I.

B. Preparation of Biofuels

Dry method was used to prepare biomass CWS and modified biomass CWS. Target concentration is calculated to determine the amount of water added. A burette was used to accurately measure a certain amount of water into a 250mL beaker, then a pipette to accurately take a certain number of additives from the reagent bottle into the beaker, using an electromagnetic stirrer at low speed. The two were mixed evenly, and a certain amount of biomass powder is added and stirred evenly. Due to high raw material particle size requirement in coal-water slurry preparation, the existing biomass debris in the laboratory is first screened, the biomass powder was obtained by sieving with a 200-mesh sieve. Then gradually adding 70g of coal powder into the beaker in this state, adjust the speed to 1500r/min, using a glass rod as an assistant, stir fully for 7min, and let it stand for a while to obtain a biomass coal-water slurry.

TABLE I

XQ coal particle size distribution parameters

The mixing of rice straw and coal powder can significantly improve the stability of CWS, which may be due to the fact that the rice straw itself contains cellulose, lignin and other main components, so that the particles in the CWS are not easy to settle, thus improving the efficiency of the slurry. body stability. With the increase of the mixing amount of rice straw, the slurry concentration decreased gradually, and the rheological index n decreased gradually, and the pseudoplastic characteristics of the slurry became more obvious

Comparing the difference in the slurry properties before and after the drying oven modification, the modification at 105 °C makes the rheological index n of the slurry increase, and the modification at 200 °C makes the rheological index n of the slurry slightly increase, that is, no modification. The pseudoplastic characteristics of the slurry prepared from rice straw were the most obvious, and the n at 105? was greater than 200?, that is, the pseudoplastic characteristics of the slurry prepared at 200? were more obvious. Treating rice straw at 105°C had little effect on other pulping properties of the pulp. Treating rice straw at 200°C increased the pulping concentration of the pulp, but the stability of the pulp became worse. When the modification temperature was 105°C, with the increase of the blending amount of modified rice straw, the change trend of the pulping properties of the slurry was the same as that in conclusion 1, but it was different at 200°C. When 1g was increased to 2g and 3g, the slurry concentration was both 66%, and the change trend of other properties was the same as Conclusion 1.

The pulping properties of the slurries prepared by the modified rice straw at 250? and 350? were compared with those prepared by the unmodified rice straw. The slurry concentration was improved, and the slurry with 7 g of rice straw was added, and the slurry concentration was not too low, 62% and 63% respectively; for the rheological properties, the slurry prepared from unmodified rice straw had the most pseudoplastic characteristics. Obviously, the rheological index n of the slurry prepared by adding 3g and 5g of rice straw to the modified rice straw at 250? increased slightly, and n<1, the slurry showed pseudoplastic characteristics, while the slurry with 7g of rice straw was added. The rheological index n>1; 350 ? modified rice straw, with the increase of the amount of rice straw, the rheological index n value of the slurry increases, only the slurry prepared by adding 3g rice straw has n < 1, the slurry The slurries exhibited pseudoplastic characteristics, and the n of other blending amounts were all > 1, showing the characteristics of shear thickening; the other pulping properties were less affected by the modification, and still had good fluidity and stability.

Conclusion

Comparing the pulping properties of CWS and biomass CWS, it can be seen that the fluidity of the slurry is good. The smaller the rheological index, and all n<1, the more obvious the pseudoplastic characteristics of the slurry, the better the fluidity and stability of the slurry, but the lower and lower the slurry concentration. The addition of rice straw is not conducive to the preparation of high-concentration biomass CWS, so the preparation of biomass CWS by temperature-modified rice straw is further explored. Modified rice straw at 105? and 200? were compared with the pulp prepared by the unmodified rice straw. The results showed that the temperature modification at 105? increased the rheological index n of the slurry, and 200 ? temperature modification makes the slurry rheological index n slightly increase, that is, the pseudoplastic characteristics of the slurry prepared from unmodified rice straw are the most obvious, and the n at 105 ? is greater than 200 ?, that is, the slurry prepared by treatment at 200 ? is the most obvious. Plasma pseudoplastic features are more obvious. The other pulping properties of the slurry prepared by treating rice straw at 105 °C were good. Although the pulping concentration of the pulp was improved when the rice straw was treated at 200 °C, the stability of the pulp was deteriorated. Therefore, the temperature modification at 105? and 200? did not effectively improve the pulping properties of the slurry. It is feasible to use the muffle furnace temperature modification method to prepare biomass coal-water slurry. The rheological index n of the slurry prepared by the modification of rice straw at 250 °C and 350 °C increases. For the same modification temperature, The more the blending amount of rice straw, the greater the rheological index n. Under the same blending amount of rice straw, the higher the modification temperature, the greater the rheological index n of the slurry. The slurry concentration of 3g and 5g increased by 3% and 2% respectively, and the fluidity and stability of the slurry were good. Therefore, the modification effect at 250? and 350? was better.

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Copyright © 2022 Muhammad Aminu Saifullahi, Hanxu Li, Facun Jiao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.