Application of energy-saving technology in carbon black production
Abstract: The production of carbon black requires a lot of space to tap its internal potential, improve the process and equipment of carbon black production, reduce energy consumption in production, turn waste generated in carbon black production into treasure, and make the production system operate safely, environmentally, and efficiently. Currently, some energy-saving technologies have been applied in the production equipment of the carbon black plant of Shanxi Coking Co., Ltd., which not only reduces the production cost of carbon black, reduces pollution, but also improves the production and operating environment. Basically realized the recycling and utilization of resources, turned waste into treasure, and reduced the emission of pollutants.
Key words: carbon black production; Energy saving technology; Waste heat utilization; Steam; Wastewater; benefit
1. Current status of carbon black production and development
Energy and the environment are the two major issues of concern in the world today, and they are also the main issues of concern for industrial development. The carbon black industry has always been a high energy consumption and high pollution industry. With the rapid development of China's automobile industry, the demand for carbon black is also increasing, which is an opportunity as well as a challenge for the development of China's carbon black industry. The development of the carbon black industry not only needs to continuously adapt to market demand and produce different types of products to meet market demand, but also needs to tap the internal potential of carbon black production, improve the process and equipment of carbon black production, reduce energy consumption in production, and turn waste generated in carbon black production into treasure under the conditions of increasing energy shortage and rising raw material prices.
2. Process Introduction
Carbon black production mainly uses coal gas and air combustion to generate high-temperature airflow. The feedstock oil of coal tar series oils is cracked at a high temperature of 1400~1500 ℃ (soft carbon black) or 1800~1900 ℃ (hard carbon black) to generate carbon black. The generated carbon black flue gas is cooled by quench water, exchanges heat with the air entering the reaction furnace and the feedstock oil to reach 280 ± 10 ℃, and enters a bag filter for collection to separate tail gas and carbon black dust, After separation, 80% of the tail gas is sent to the tail gas boiler for steam production through a pressurized fan, and 20% is sent to the tail gas combustion furnace for drying the carbon black particles after wet granulation. The dust separated from the bag filter passes through the micron pulverizer through the air blower, and then through the wet granulator to produce granular products, which are dried and sent to the product bin.
From the perspective of carbon black production process, carbon black requires a large amount of coal tar series feedstock oil and gas, and indirectly consumes a large amount of power energy such as water, electricity, and steam. Therefore, energy-saving technology in carbon black production is very important.
3. Application of carbon black energy-saving technology
Taking the production of carbon black in Shanxi Coking Co., Ltd. as an example, the discussion and analysis were conducted. The company currently has a soft carbon black production line with an annual output of 20000 tons and two hard carbon black production lines with an annual output of 30000 tons, both designed by China Rubber Design Institute. The hard production line has two online waste heat boilers, 850 ℃ high-temperature air preheaters, high-efficiency pulse bag filters, and wet granulation machines, which incorporate energy-saving processes into the production process. Mainly reflected in the following aspects:
3.1. Make full use of process waste heat
Install an online air preheater to preheat the air to about 830 ℃, and then heat it further through the reactor jacket before entering the reactor. The temperature of the feed oil reaches 220 ℃ after being preheated by the flue gas, thereby strengthening the reaction conditions, reducing primary energy consumption, recovering the secondary energy generated during the process, and effectively reducing the unit consumption of carbon black production.
Application of air preheater. The normal temperature of the air is 20 ℃, and the carbon black flue gas is preheated to 830 ℃. The recoverable process waste heat is: the amount of air entering the furnace is calculated as 14000 Nm3/h, and the specific heat of air is Cp=(1.013+1.114)/2=1.064 kJ/kg. ℃ M=CpP=0.816 kJ/m3. ℃
Hourly absorption of residual heat: Q=CpM Δ T=0.816x14000x (830-20)=9.25x106kJ If steam is used for preheating: 0.5MPa, the latent heat of vaporization of low-pressure steam is 2108kJ/kg, and steam N is required:
N=9.25x106/2108=4.39x103kg=4.39t
Steam required for two production lines: 4.39x2=8.78t
Based on the calculation of 130 yuan per ton of steam, 1141.4 yuan can be saved per day.
B. Use waste heat boilers to recover waste heat and produce steam
In order to fully utilize the waste heat of flue gas, this device is equipped with a 4t/h low-pressure steam online waste heat boiler, which generates steam that is incorporated into the steam system, saving 4t of low-pressure steam per hour. Based on the consumption of 200 Nm3 of gas per ton of steam, 800 Nm3 of gas can be saved per hour. The two production lines are 1600 Nm3, and based on the calculation of 0.265 yuan/Nm3, 424 yuan can be saved per hour.
Application of raw oil preheater
After preheating with flue gas, the temperature of raw oil can rise from 90 ℃ to 200 ℃, and the raw oil can be controlled within 5000~7000 kg/h based on product quality.
The specific heat of raw oil is calculated as 2.10kJ/kg, and the amount of raw oil is calculated as 6000kg/h. The required heat absorption is:
Q=CpM Δ T=2.1x6000x (200-90)=1.39x106kJ If steam is used for preheating: 0.5MPa, the latent heat of vaporization of low-pressure steam is 2108kJ/kg, and steam N is required:
N=1.39x106/2108=0.66x103kg=0.7t
The steam required for the two production lines is: 0.7x2=1.4t Annual steam savings: 1.4x24x365=1.22x104t. Based on 130 yuan per ton of steam, 1.58 million yuan can be saved annually.
3.2 Recovery and utilization of carbon black tail gas
Carbon black tail gas is about 48000 Nm3/h, with a calorific value of Qdy=2658.62 kJ/Nm3, of which 20% is used for drying after wet granulation, and the remaining 80% is sent to the tail gas boiler to generate steam. Utilizing the heat of tail gas can save 133t standard coal per day, and achieve better economic and environmental benefits.
Tail gas combustion furnace
The tail gas furnace uses about 20% tail gas. About 9600Nm3/h, generated heat Q=9600X636X4.1868=25.56X106kJ, and gas calorific value is 16200kJ/Nm3
Hourly gas saving: 25.56 × 106/16200=1578 Nm3
The two production lines are: 2X1578=3156Nm3, that is, the cost savings per hour: 3156X0.265=836.34 yuan.
Application of 45 t/h boiler
The boiler uses 80% of exhaust gas. About 38400Nm3/h, generated heat Q=38400X636X4.1868=102.25X106kJ, and gas calorific value is 16200kJ/Nm3
Hourly gas saving: 102.25X106/16200=6312Nm3
The two production lines are: 2X6312=12624Nm3, that is, the cost savings per hour: 12624X0.265=3345.36 yuan.
3.3 Tail gas, soft water, circulation, equipment, recovery
Through sealing modification of the top cover of the bag filter box, tail gas leakage is reduced; By changing the inlet and outlet valves of the bag filter from the original butterfly valve to a gate valve, it is convenient to replace the filter bag in a timely manner after the bag filter leaks, which not only reduces environmental pollution, but also extends the service life of the filter bag; The soft water used to cool the soft raw material oil gun is recycled for use in hard waste heat boilers and process water fed into the reaction furnace; By evaluating the materials of the easily corrosive bag filter box and air supply pipeline, increasing the material thickness not only reduces the leakage of the box, but also extends the service life of the equipment. Recycle and filter the on-site external drainage, and recycle it for washing the ground at the production site to improve the on-site environment; The steam condensate from the production site is collected centrally, cooled, and then recycled to the process water tank for recycling for production. According to statistics, after a series of transformation measures, the wastewater at the production site has basically achieved zero discharge, with a monthly saving of 400 tons of process water. Based on the calculation of 2.2 yuan per ton of industrial water, a monthly saving of 880 yuan can be achieved; Soft water recovery can save 40 tons per day, and based on 10 yuan per ton of soft water, the cost can be saved by 400 yuan per day; Through the transformation of tail gas, more than 5000 Nm3/h is recovered, with Q=5000 × 636 × 4.1868=13.31 × 106kJ, saving 13.31 × 106/16200=822 Nm3 of gas per hour, i.e. saving cost per hour: 822 × 0.265=217.83 yuan.
3.4 Application of other energy-saving technologies
Insulating the air pipeline into the reaction furnace can reduce product unit consumption and stabilize production; Using frequency conversion control for the gas regulating valve of the induced draft fan of the tail gas boiler can effectively save electricity consumption; Reforming the relay of the air blower can reduce frequent trips caused by current fluctuations, reduce environmental pollution, and so on.
