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Li Heng, Cui Qingsong, ShiLe, Yuan Yu, Li Zhijie
(Great Wall Motor Co., Ltd. Technology Center, Hebei Automotive Engineering Technology Research Center, Hebei, Baoding 071000)
Introduction
With haze pollution, the state has stepped up efforts to clean up environmental protection regulations, environmental protection regulations on emission standards are also increasingly stringent
. In recent years, enterprises involved in emissions have gradually increased their environmental treatment equipment to cope with the environmental pollution caused by exhaust gases. However, whether the equipment planning selection is reasonable in the equipment operation process gradually reflected, with environmental protection equipment, equipment operation and consumption has become a major input to the workshop economy, directly increasing the cost of a single vehicle . This paper combs according to the design planning, post-operation input and safety problems of exhaust gas treatment equipment, and introduces the design and selection of exhaust gas treatment equipment.
1
Introduction to exhaust gas treatment equipment
How the exhaust gas treatment equipment works: workshop exhaust gas temperature control and humidification by filter, sent to the wheel for concentrated filtration emissions, with high temperature air adsorption on the wheel
VOC
for high-temperature dissociation, de-attachment of high concentration of gas in high temperature environment for high-temperature incineration treatment.
automobile coating workshop as the main source of exhaust gas generation, the current coating workshop generally adopted exhaust gas treatment is zeolite wheel concentration and high concentration
VOCs
incineration treatment. The equipment forms of zeolite concentrated wheel plus
TAR
" and "zeolite concentrated wheel plus
rTO
" are generally used in the field. According to the workshop exhaust gas volume, exhaust gas concentration and site site constraints, the layout of the site is different.
2
Introduction to exhaust gas treatment structure
Exhaust gas treatment equipment in the structure and function can be divided into three parts: the pre-treatment part before the wheel, the zeolite wheel enrichment part, the exhaust gas incinerator part.
pre-treatment part of the wheel: the pre-treatment before the wheel is divided into temperature adjustment and humidification and filtration part. Temperature control and humidification is mainly for the paint workshop using Venturi water curtain treatment before the discharge of exhaust gas with low temperature and high humidity (temperature
20
degrees C
to 30
degrees C, humidity
80% To 95%
or so) characteristics to take a heating and humidification way to improve the temperature of the air before the wheel to reduce the moisture content of the air to reach the wheel optimal adsorption temperature humidity (temperature
40
degrees C, humidity <
90%
) state. The filtration part removes the large particulate matter from the wheel by using different levels of filter combination, so that the wheel
the
VOCs.
the concentrated part of the zeolite wheel: the zeolite wheel part is divided into three regions according to the function, the adsorption area, the dissoction area, the cooling area. The drive motor drives the wheel rotation through the chain drive and adjusts the processing efficiency of the zeolite wheel by adjusting the speed of the wheel. The adsorption zone will filter the exhaust gas of the workshop, and the adsorption of benzene, toluene, xylene, ethyl acetate, butylone, isopropyl alcohol and ether in the exhaust gas is used to absorb the gas in the wheel. Filtered and discharged directly, the van der Waru and electrostatic attraction between zeolite molecules and
VOCs
molecules in the wheel are destroyed at a temperature of about 200 degrees C.
VOCs
concentrated into a high concentration
5 to 20
of the original gas. The cooling zone cools the wheel temperature through a low temperature wind for the next stage of exhaust gas adsorption.
exhaust gas incinerator:
VOCs
fracking provides a high temperature environment of
750
degrees C
to 800
degrees C, where
VOCs
and oxygen oxidation react to produce carbon dioxide and water and release large amounts of heat. At present, there are
TAR
, bed
RTO
and rotation
RTO
three common on the market, design and selection according to the field exhaust gas volume, exhaust gas concentration, heat demand for later use, site and post-use maintenance costs and other comprehensive considerations to choose.
3
On-site program introduction
3.1
economic introduction
exhaust gas treatment itself as a high energy consumption equipment, its early design and planning directly affect the economy of later use, such as involving unreasonable by a significant increase in the economic costs of operation. The operating energy consumption of exhaust gas treatment equipment can be considered in the following aspects.
3.1.1
filter material loss
the workshop to adopt a coating process is different, emissions are not the same. The exhaust gas of the coating workshop has the characteristics of high wind volume and low concentration. In order to protect the wheel, the exhaust gas before entering the wheel needs to be filtered before entering the wheel. The filter material selection filtration accuracy before the wheel does not meet the requirements, the long-term operation will affect the wheel processing effect, reduce the wheel processing efficiency, resulting in the wheel processing effect is not up to standard. For dry spray room, the exhaust gas humidity is small, its filtration requirements for exhaust gas is relatively low, exhaust gas can be simply moisturizing. For wet Venturi structure spray room, the exhaust gas impurities are relatively large, the primary filter is changed frequently, and the input cost of filter material replacement is larger. Failure to replace in time may result in a risk of the filter blowing down.
for wet paint chambers, the pre-treatment structure design of exhaust gases before entering the filter needs to be considered. Such as increasing the use of large dust filter bags or the use of metal mesh or maze filter in the exhaust gas of large particulate matter for preliminary filtration, the use of the collision of substances to form small particulate matter large particulate matter, regular flushing of the initial filter or compressed air blowing. Reduce the rate of filter contamination, reduce the number of filter changes, reduce the cost of filter material use.
3.1.2
gas consumption
mainly reflected in the exhaust gas incineration options. The incinerator provides heat from natural gas as raw material to provide a high temperature environment for exhaust gas treatment. Let the exhaust gas oxidize and decompose. The choice of combustion chamber should be considered in terms of whether the heat and on-site exhaust gas concentration, investment cost and floor area of the whole system later stage need to be considered. For
RTO
system, the exhaust gas concentration of
RTO
reaches
1.8g
to achieve self-holding combustion of the operating process and "zero" consumption of the exhaust gas incineration system. This requires a comprehensive measurement of the exhaust
, wheel
, etc. before entering the RTO before the equipment is selected. There are many methods to increase the concentration of exhaust gas: such as painting room wind part of the work surface circulation wind for re-use, improve the wheel concentration ratio, wheel concentration after the exhaust gas for re-wetting and so on. But at the same time, it is necessary to consider the risk of explosion caused by the super-temperature of the wheel and the concentration of de-attached exhaust gas. For
tar
selection, the heat used in the 1st stage equipment should be taken into account, such as the use of waste heat recovery devices, so that all the heat generated by
TAR
is used by the later stage equipment.
3.1.3
energy consumption
energy in the exhaust gas treatment system is mainly wind electromechanical energy consumption. Therefore, in the process of equipment pre-design, we must first consider the distance between exhaust gas treatment equipment and the exhaust gas source of the workshop, reduce the length of the duct, reasonably calculate the amount of wind, reduce the amount of wind entering the exhaust gas treatment, reduce the number of wheels, avoid the waste of electricity caused by excess equipment selection; In addition, timely replacement of equipment filter material, reduce wind pressure caused by the wind turbine operating frequency is too large to cause waste of electrical energy.
3.2
Safety Introduction
exhaust gas treatment equipment involves exhaust gas concentration safety mainly related to wheel and
RTO
safety.
equipment as a whole needs to consider the concentration of exhaust gas in the de-attached line, the pipeline set
exhaust gas concentration detector timely feedback in the pipeline exhaust gas concentration, when the concentration exceeds the standard timely mixed with the new wind drop concentration emissions.
zeolite wheel as an important part of zeolite concentration, its main components are mainly zeolite and fiber paper for the substrate processing. Fiber paper is the most sensitive to temperature changes, so temperature should be taken into account in design and options. The temperature control of high temperature gas in the de-attached area of zeolite wheel is precise, so the valve selection is more demanding. In terms of selection, consider using a one-time wind or cooling wind in the form of secondary heat exchange to meet the high temperature dissocation temperature requirements. The design should take into account the sealing of the high temperature valve, the mixed air uniformity of the mixing tank and the location distance between the mixing tank and the disembed area, to minimize the high and low temperature wind mixing method to obtain the dissocing wind, once its control is not good easy to produce the risk of wheel fire.
exhaust gas treatment system should be designed to take full account of the valve selection in the pipeline, and the pipeline in contact with the high concentration of exhaust gas should use explosion-proof valve and pneumatic wind valve. Part of the position to use self-return valve, the system facilities gas storage tank, the system after the system power down to reduce the flow of hot air to flammable areas, eliminate the risk of fire.
the
system equipment to take into account the incinerator before ignition pre-blow sweep and the equipment as a whole explosion-proof, the system needs to set up explosion-proof port. The system needs to set up a high temperature emergency discharge port, when the exhaust gas concentration is too high to consider some high temperature flue gas for chimney discharge.
3.3
Other
1)
For the coating workshop exhaust gas source part is different, in the zeolite wheel selection should be clearly proposed, according to different seats, different components of exhaust gas in the rotation to design different types of wheel.
, for example, water-based paint in a face position is different from solvent-based paint, the mixing process produces
N, N-
dymethylethanolamine substances, prone to the risk of clogging the wheel, so surface water-based paint and solvent varnish produced by the
VOCs
should be configured with wheel treatment.
2)
the amount of exhaust gas treated by exhaust gas treatment equipment is very large, in the selection process of equipment needs needle factory location and the impact on the surrounding residents have different noise demand. Equipment needs to consider increasing the noise of high-powered fan, such as setting up facilities such as silencer rooms and silencer walls, to eliminate the noise effects of fan.
4
April
, 2018, the state began to tax environmental emissions, and the on-line monitoring system for exhaust gases will be put into use. As the main part of exhaust gas treatment, the operational stability of exhaust gas treatment equipment directly affects the effect of exhaust gas treatment. In the process of equipment selection, we should start from the point of view of equipment stability, safety and economy. Choose a reasonable exhaust gas treatment process to meet emission standards while taking into account the energy consumption of the equipment operation. In the use of the process of continuous accumulation of experience, so that equipment better for production and environmental protection services.
content source: Modern Coatings and Coatings