Principle of regenerative thermal oxidizer (RTO)
The regenerative heat exchanger is a heat exchanger with heat storage material filling inside; The two gases pass through the filling alternately and store the heat to be transferred temporarily. This kind of filling material that can let gas pass through and store heat is called heat accumulator.
Generally, heat exchange is carried out by cold and hot fluids. When the hot gas passes through the heat storage body in a certain time, its heat is transferred to the heat storage body (thermal cycle), and the heat storage body is heated to a certain degree; At the same time, it is colder to pass through the heat accumulator of the other set. In addition, the heat obtained by the heat accumulator during the hot cycle will be recovered again (cold cycle). At the end of a cycle (cycle), change the direction of gas flow, so that a hot accumulator is cooled by cold gas; The other cooler regenerator is heated by hot gas. Generally, the duration of the hot cycle is equal to the duration of the cold cycle, which is called the commutation time or switching time; The hot cycle plus the cold cycle is called the full cycle. The duration of the full cycle is twice the switching time.
The regenerative thermal oxidizer (RTO) used in the thermal combustion purification of organic waste gas is the principle of using the principle of regenerative heat exchanger mentioned above.
So far, RTO has been used in organic waste gas purification for more than 30 years, with mature technology and common application. The reason is that many advantages of RTO are as follows:
(1) Almost all waste gases containing organic compounds can be treated;
(2) It can handle organic waste gas with large air volume and low concentration;
(3) The flow of organic waste gas is very flexible (from 20% to 120% of the nominal gas flow);
(4) It can adapt to the change and fluctuation of VOC composition and concentration in exhaust gas;
(5) Not sensitive to a small amount of dust and solid particles in the exhaust gas;
(6) Among all thermal combustion purification methods, the thermal efficiency is the highest (>95%)
(7) Under the condition of appropriate gas concentration (generally>2 〜 3g/m ³, It depends on the calorific value of VOC) to realize self-heating operation without adding auxiliary materials;
(8) High purification efficiency (three rooms ＞ 99%, two rooms 95% 〜 98%);
(9) Less maintenance work, safe and reliable operation.
(10) Organic sediments can be removed periodically, and the heat storage body can be replaced;
(11) The pressure loss of the whole device (the total pressure loss of the RTO device system is generally less than 3000Pa, which varies with the structure type and gas integrity of the used heat accumulator);
(12) The service life of the device is long.
No matter how many advantages are, they are relative. The key is that although the purification of organic waste gas with RTO is not once and for all, there are few troublesome things in production management, operation and maintenance.
Main disadvantages of RTO:
(1) The device is heavy (due to the use of ceramic heat storage)
(2) Large device volume (therefore, large devices can only be placed outdoors)
(3) It is required to operate continuously as much as possible (restart takes a long heating time, although the current technical level can shorten the heating time);
(4) The investment cost is relatively high.
In order to realize continuous operation, in principle, two regenerative heat exchangers (also known as regenerative chamber or regenerative furnace) are required. Even the so-called single regenerative furnace actually divides the bed of the regenerative body into a central reaction zone and two (or left and right) alternating cooling/heating zones. Of course, it is also possible to rotate the heat storage body without changing the gas flow direction; Alternatively, the heat accumulator can be fixed, and the continuous operation can be realized by rotating the gas distribution hood (air distributor) to change the gas flow direction. According to these different structural principles, many different types of RTOs can be formed.