Analysis of the causes of blockage in RTO incinerators in the pharmaceutical industry

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In pharmaceutical industry RTO burners, as operating time increases, the system negative pressure deteriorates, the fan load rises, and the air volume decreases significantly. Under normal operation, the pressure difference between the inlet and outlet of the RTO system is 4000 Pa; as blockages accumulate, this pressure difference rises to around 7000 Pa. At the same time, the online monitoring data for total non-methane hydrocarbons at the RTO exhaust outlet was about ten milligrams per liter higher than the normal value. The reason for this phenomenon is that the heat storage material becomes clogged, and these blockages affect the sealing performance of the lift valve, resulting in a small amount of exhaust gas escaping untreated. To ensure the effective processing capacity and performance of the RTO, it is necessary to shut down the RTO, cool it down for inspection and cleaning, which in turn affects the normal operation of the RTO system. A company analyzed the composition of the substances that clogged the RTO combustion chamber and ceramic regenerators; the main cause was indeed salt deposition. Taking into account all the factors contributing to the formation of these blockages, there are mainly four reasons: (1) Large amounts of waste gas containing acidic and alkaline components are emitted from the workshop and enter the RTO’s main ducts, where acid-base reactions occur to form salts. These salts, along with other particles present in the waste gas, accumulate on the pipe walls, the pre-heater fans, the mist eliminators, the flame arresters, and the lower chambers of the regenerators. Although mist eliminators are installed in front of the RTO combustion chamber or the induced draft fan, the wind speed in the main ducts is too high to remove the mist completely. The presence of acids, bases, and salts caused severe corrosion in the main pipes and mist eliminators; even the RTO regenerators were affected by corrosion and flaking. The flaking of elements such as iron, silicon, and aluminum exacerbated the blockage in the lower chamber of the RTO regenerators. (2) The exhaust gases generated by the wastewater treatment system contain trace amounts of dust and sludge particles (microorganisms); the sludge also contains organic matter, water, salts, phosphorus, and other substances. Upon entering the RTO, these substances adhere to the surface of the induced draft fan, and after combustion, the inorganic substances stick to the surfaces of the ceramics and the combustion chamber. Furthermore, the exhaust gases generated in the anaerobic and facultative aerobic stages of wastewater treatment contain not only methane but also organic acids, large amounts of ammonia, hydrogen sulfide, and other gases. At high concentrations, the salts and sulfides produced can easily cause blockages at the inlet and outlet of the RTO regenerator. (3) The exhaust gas is burned in the RTO combustion chamber; sometimes, when the concentration and calorific value of the exhaust gas are high, the temperature of the upper part of the RTO can exceed the limit, reaching over 1,050 °C. In such overheated conditions, the ceramic heat storage material can be damaged, and the resulting fragments increase the bulk density, reducing the flow rate of exhaust gas and thereby increasing the load on the fan as well as deteriorating the system’s negative pressure. (4) Exhaust gases containing P, S, and halogen gases generate acidic gases after combustion in an RTO. Some RTO systems are designed to use exhaust fans to draw in the hot exhaust gases from the chamber and use them to preheat the incoming air at the front end of the combustion chamber; these acidic gases can cause corrosion to the RTO combustion chamber, the flue gas outlet equipment, the exhaust fans, and the inlet pipes of the combustion chamber. Iron sulfate, iron chloride, and other substances resulting from these corrosion reactions accumulate within the RTO chamber and the ceramic regenerators.