Application of RTO in the treatment of organic was

Analysis on the application of RTO in the treatment of organic waste gas in pharmaceutical industry

the components of waste gas in pharmaceutical industry are complex, including benzene, toluene, ethanol, ethyl acetate, hydrogen chloride, etc. Among them, benzene ring and halogen are easy to produce dioxins at about 400 ℃. Dioxins are very stable, with high melting point, very difficult to dissolve in water, and are colorless and tasteless fat soluble substances, so they are very easy to accumulate in organisms and do serious harm to human body. The corrosion of dioxin and acid gas is the key to distinguish the pharmaceutical industry from other industries

1 project background

take a pharmaceutical factory in Zhejiang as an example: the maximum air volume of waste gas is 20000nm3/h, and the concentration of waste gas is about 2000mg/m3. The main components are as follows: acetic acid, toluene, DMF, chloroform, ethyl acetate, methanol, N-methylpiperazine, tetrahydrofuran, acetone, dichloromethane, benzene, acetonitrile, cyclohexane, isopropanol, dimethyl sulfoxide, methyl isobutyl ketone, triethylamine, hydrogen chloride, monochloromethane, acetic acid, ammonia and other components

2 process selection

waste gas belongs to small air volume and medium concentration waste gas, most of which are organic waste gas and contain some acid gas. A more reasonable process is: washing +rto+ washing. Dioxins cannot be avoided in RTO at this time. However, dioxins can be decomposed when the temperature is higher than 850 ℃ and the combustion time is greater than 1s, or when the temperature is higher than 800 ℃ and the combustion time is greater than 2S. Dioxins will not be produced after the benzene ring is destroyed, that is, the reaction is irreversible, so our furnace design combustion temperature is 850 ℃ and the combustion time is more than 2S

3 process flow chart

rto principle: the regenerative thermal oxidation furnace professionally processes organic waste gas, so that the organic waste gas can be decomposed completely in a high-temperature environment, with a decomposition rate of more than 98%, and finally the waste gas emission meets the national environmental protection standards. The thermal oxidation furnace uses two fixed heat exchange media beds. The heat exchange media uses heat storage ceramics, and the exhaust gas from the production line is heated after passing through a thermal ceramic media bed; According to the industrial research center of Liaohe Zhongtou Investment Consulting Co., Ltd., the high-temperature gas burned behind the bore heats the other heat exchange medium bed. In this way, the two heat exchange medium beds switch to each other, and heat the low-temperature exhaust gas after heat storage. The heat exchange efficiency reaches more than 95%. It is easy to use organic waste gas to realize the self-sustaining of the oxidation furnace without any fuel. In order to improve the efficiency of waste gas treatment, we use three tower RTO

4 equipment introduction

4.1 regenerative oxidation furnace

rto device the reaction equation of organic matter degradation in the combustion chamber is as follows:

our RTO equipment is a three bed RTO equipment independently developed on the basis of German and American technology. The system is mainly composed of combustion chamber, three groups of regenerative beds with the same structure, three pneumatic switching inlet valves, three pneumatic exhaust switching valves and three pneumatic purge switching valves, The 9 pneumatic switching valves are switched automatically, with a switching cycle of 1-6min, which is controlled by time. If the outlet temperature exceeds the set value, it will be switched forcibly. The heat storage bed is filled with regular honeycomb ceramic heat storage body. Its main material is dense cordierite, which has excellent corrosion resistance to acid, alkali and organic media, good heat storage effect, high heat recovery efficiency, low wind resistance, small thermal expansion and contraction coefficient, good crack resistance, long service life and other advantages. The internal lining of the equipment is made of high-temperature resistant ceramic fiber insulation materials with a thickness of more than 300mm, which can fully ensure that the surface temperature of the equipment is lower than the national standard, and can effectively prevent gas from contacting with steel components. Pneumatic switching valves are all pneumatic actuators of well-known brands. Among them, the pneumatic switching valve body is made of duplex stainless steel, which has stable switching and long service life, and can be switched for 10million times in normal operation. To prevent the corrosion of the parts in contact with the steel plate of the furnace body. The parts in contact with the exhaust gas are lined with anti-corrosion paint, and the spraying materials are resistant to high temperature, which can ensure the long service life of the furnace body. In the process of daily maintenance, if the coating falls off, it needs to be repaired in time to prevent large-area oxidation

4.2 alkali washing purification tower

alkali washing purification tower has the characteristics of low resistance, low energy consumption, low noise, high processing efficiency, and can process hydrogen chloride gas, hydrogen fluoride gas, ammonia mist, chromic acid mist, hydrogen cyanide gas, alkali vapor, hydrogen sulfide gas and other gases. It has the characteristics of high purification efficiency, small floor area, good corrosion resistance, aging resistance, and light weight. It is suitable for discharging corrosive acid mist gas with a certain concentration, and is mainly used in chemical industry, electronics, hospitals, research centers and other places

working principle: after the waste gas to be treated is pressed into the inlet section of the purification tower by the glass fiber reinforced plastic centrifugal fan, it vertically reacts with the liquid in the spray section from top to bottom to reduce the concentration of the waste gas, and then continues to enter the packing section upward. The waste gas rolls in the plastic ball and neutralizes with the absorption liquid to further reduce the concentration of the waste gas before entering the dehydrator, and the purified gas is discharged into the atmosphere. Through measurement and analysis, the purification efficiency of sulfuric acid mist can reach 93%, nitric acid purification efficiency can reach 90%, hydrochloric acid mist purification efficiency can reach 98%, and the purification of acid mist has reached the domestic advanced level. The alkali washing purification tower is a cylindrical structure. The whole tower is composed of three parts, namely, liquid storage, air inlet, spray, dehydration and air outlet. The outlet pipes are connected, and the plastic balls are respectively installed in the spray. The alkali washing purification tower is made of glass fiber reinforced plastic, with compact structure, corrosion resistance, high temperature resistance and smooth appearance; Water vapor separation occurs in the water removal part; Water spray Department: high pressure water spray produces fog, which is divided into upper and lower sections to expand the contact treatment and improve the function; Filler: plum blossom ring or Bauer ring, PP material is integrated, and anti overflow discharge pipe is required; Observation window: made of 5mm thick transparent acrylic plate

5rto safety design

a. impact of fire in the pipeline on the workshop: most of the explosion in the pipeline comes from the sudden volatilization of a large amount of organic liquid in the pipeline, and then meets with static electricity. It is difficult to make anti-static facilities for pipelines transporting corrosive gases, which can only reduce the wind speed. The wind speed designed below 8m/S is more suitable

o impact of fire on the workshop: it is difficult for open fire in RTO furnace to enter the pipeline from the workshop, because there are about 2 meters high heat storage ceramics, and the heat storage body itself is a good flame arrester. Flame arresters can be installed at the front of the pipeline to further ensure the safety of the production workshop

o: RTO should be purged before ignition. The purpose of purging is to clean up the organic matter left in RTO pipes and furnace to avoid detonation during ignition. There is a concentration detector at the RTO inlet, and the response time is about 5 seconds, so the installation position of the concentration detector is relatively important, and a buffer tank should be made. When the alarm of high exhaust gas concentration is detected, the fresh air damper will automatically open for concentration dilution; If the high concentration of waste gas will alarm, RTO will cut off the connection with the production line, and the waste gas will be directly bypassed to the chimney. In actual production, no amount of measures can be taken to 100% avoid explosion, so add explosion relief devices at appropriate positions. For example, there is a explosion relief door on the top of RTO furnace, which can be closed by its own weight, and the normal operation of RTO will not be affected after explosion relief; The buffer tank is provided with explosion relief sheet. With these explosion venting measures, even if there is an explosion, the loss of explosion will be minimized

d. design of emergency power failure system: RTO is very afraid of sudden power failure, and the high temperature in the furnace cannot be dissipated quickly, resulting in high temperature damage to many anti-corrosion materials or other equipment. We have designed an emergency compressed air storage tank, ups and manually and automatically controlled explosion relief valve. In case of sudden power failure, ups and emergency compressed air storage tank will turn all dampers to safe positions, such as fresh air damper open, purge damper open, explosion relief valve open, etc; The emergency compressed air will enter the burner pipe to avoid the leakage of high-temperature flue gas from the burner, resulting in the danger of ignition pipeline and damage to the burner. However, compressed air and even several weather tanks can only support for about 15 to 20 minutes. Party A needs to configure standby power supply for compressed air or combustion supporting fan

e. high temperature protection of the system with a washing tower at the RTO outlet: the RTO outlet is connected to the washing tower. If the washing tower is made of FRP, the RTO outlet temperature needs to be controlled below 100 ℃. If it exceeds 100 ℃, the RTO will automatically cut off the connection with the production line, and the process waste gas will directly enter the chimney

g. furnace over temperature protection: there are two thermocouples in the furnace, each of which is double. If one of them has problems, there is another one for standby to ensure uniform temperature control in the furnace. The furnace temperature cannot exceed 980 degrees Celsius, otherwise the service life of the internal heat storage ceramics and ceramic fiber blocks will be affected. When the furnace temperature exceeds a certain value, the double solenoid valve of the fuel pipe will automatically close to prevent diesel oil from leaking into the furnace. If the furnace temperature is higher, open the fresh air damper to cool down. When the furnace temperature alarm occurs, RTO will automatically cut off the connection with the production line, and the process waste gas will directly enter the chimney

6rto

when the operation process is started for the first time, it is necessary to preheat the heat storage body. After preheating to the set temperature, the waste gas containing volatile organic compounds (VOCs) enters the heat storage bed through the switching of valves. The waste gas is gradually heated by the heat storage ceramics and then enters the combustion chamber (the combustion chamber has two functions: one is to ensure that the waste gas can reach the set oxidation temperature, the other is to ensure that the waste gas has sufficient residence time, so that the VOCs in it can be fully oxidized), VOCs oxidize and decompose at high temperature in the combustion chamber and release heat. When the hot air formed passes through another heat storage bed, it exchanges heat with the heat storage body to accumulate heat, so as to reduce the consumption of auxiliary fuel, and the temperature of oxidized clean gas gradually decreases. During normal operation, RTO internal temperature control is realized by burner. When the concentration of organic waste gas reaches the self-sustaining combustion state, and the heat generated is enough to meet the requirements of the next cold air preheating, the system can complete the oxidation of organic waste gas without turning on the auxiliary heating device for auxiliary heating, so as to achieve the effect of energy saving. When the RTO temperature is abnormal (i.e. the front-end concentration is too high), close the inlet valve automatically through PLC program, and fully open the abnormal discharge and fresh air valve, so that the RTO equipment can be completely cooled by fresh air. RTO furnace temperature is monitored in real time by two high-temperature thermocouples. During operation, PLC program controls the stability of furnace temperature by automatically adjusting the gas regulation ratio and relevant valves. In case of abnormal temperature rise in the furnace, the emergency temperature discharge can be carried out through the temperature relief port of the RTO equipment that cannot impact the normal temperature

7rto cost operation analysis

the main costs of the facility during operation are power consumption and natural gas, as well as some maintenance costs, such as the replacement of pre filtration materials. See Table 1 below for the estimation of operation cost:

(1) the main fan, combustion supporting fan and pump are calculated as 16h/d and 250D/A; The electricity charge is 0.75 yuan/kwh, the actual power of the motor is 0.8 of the rated power, and the energy saving of the variable frequency fan is calculated as 0.70

(2) the cost of preheating the RTO equipment for the first time and maintaining the furnace temperature after the introduction of waste gas, each preheating time is calculated as 3 hours, and the annual preheating is calculated as 12 times; Considering the need for supplementary heating due to low concentration during production and operation every day, the daily supplementary natural gas volume is 20 cubic meters, and the natural gas used for each heating is 50 cubic meters. The price of natural gas is 2.5 yuan per cubic meter

when the concentration of exhaust gas reaches 2800mg/m3, the system can maintain self-operation without supplementary natural gas heating