Ship coating is one of the severe pollution sources in the shipbuilding industry. During the sectional coating manufacturing of large ships, organic solvents are always used, together with a certain proportion of thinners. A large amount of organic waste gas is generated in the processes of spraying, leveling and drying. Among the waste gas, benzene-containing organic substances are highly toxic, which not only harm the physical health of construction workers, but also pollute the surrounding atmospheric environment.
The main components of waste gas from ship coating include benzene, toluene, xylene and so on, as well as a certain amount of paint mist. Therefore, paint mist must be removed before waste gas treatment.
Brief Introduction to Treatment Processes for Ship Coating Waste Gas：
For organic waste gas from ship coating, traditional technologies such as photocatalysis, low-temperature plasma and photo-oxidation were once mainstream processes for organic waste gas treatment. However, due to unsatisfactory treatment effects and the secondary pollution problem of ozone in tail gas, these technologies have been gradually phased out in the market. The major processes for treating organic waste gas from ships include Regenerative Thermal Oxidizer (RTO), Regenerative Catalytic Oxidation (RCO), zeolite rotor adsorption and desorption coupled with catalytic combustion, activated carbon adsorption and desorption coupled with catalytic combustion, etc.
1.Regenerative Thermal Oxidizer (RTO)
This technology adopts thermal oxidation to treat organic waste gas, and is applicable to the treatment of large-air-volume, medium-low-concentration organic waste gas with complex components. Ceramic regenerative bed heat exchangers are used to recover heat. The regenerative beds switch directions alternately through reversing valves, store heat from high-temperature gas discharged out of the combustion chamber, and preheat the organic waste gas entering the regenerative beds. The organic waste gas preheated to a certain temperature (≥760℃) undergoes oxidation reaction in the combustion chamber to generate harmless carbon dioxide and water for purification. There are various types of RTO, including two-chamber, three-chamber, five-chamber and rotary RTO.
Advantages: Treatment efficiency ranges from 95% to 99%; heat recovery rate exceeds 95%; the equipment has a moderate volume; fully automatic operation with simple and convenient operation; no leakage during switching.
2.Regenerative Catalytic Oxidation (RCO)
With the effect of catalysts, this technology decomposes VOCs into CO₂ and H₂O at a low temperature of 200~400℃, serving as one of the effective means to purify hydrocarbon waste gas and eliminate malodors. This technology can also be applied to activated carbon adsorption concentration and catalytic combustion systems to replace the catalytic combustion and heater parts.
Advantages: Treatment efficiency reaches 95~99% with high removal efficiency; no secondary pollution; wide application scope and adaptability to various working conditions; stable conversion efficiency and reasonable air flow distribution to guarantee the effectiveness of explosion-proof measures; low ignition temperature and flameless combustion reduce open flames, which saves energy and greatly improves safety at the same time.
3.Zeolite Rotor Concentration + Incinerator
This technology utilizes the characteristic that zeolite with specific pore sizes can adsorb and desorb organic pollutants. It converts large-air-volume and low-concentration VOCs waste gas into small-air-volume and high-concentration gas, which is then incinerated to thoroughly purify the waste gas.
Advantages: The pressure drop generated by adsorption is extremely low, which can greatly reduce power energy consumption; the concentration multiple reaches 5 to 25 times, greatly downsizing the specifications of post-treatment equipment and lowering operating costs; the overall system adopts modular design requiring small space, and supports continuous and unmanned operation mode; the system is automatically controlled with one-key startup and simple operation, and can be equipped with a man-machine interface for monitoring.
4.Activated Carbon Adsorption and Desorption
This method relies on the strong adsorption capacity of activated carbon itself to adsorb organic waste gas molecules on its porous surface. This technology can efficiently absorb various organic waste gases and is suitable for the treatment of large-air-volume and low-concentration waste gas.
Advantages: Convenient maintenance with low manpower requirements; large specific surface area capable of treating multiple mixed waste gases simultaneously; activated carbon features wide sources and low prices; simple operation.
In conclusion, there are various treatment processes for tail gas generated by ship painting. We shall select the suitable process for treatment in combination with the actual conditions of the owner and the site.
