Tailgas combustion
Claus plants are used to convert H2S from natural gas and crude oil into liquid sulphur. For this purpose, the H2S-containing waste gas (Claus gas) is burnt sub-stoichiometrically in several stages, depending on the process.
For reasons of efficiency, not all of the H2S gas from the exhaust gas can be converted to sulphur. In order to prevent the small amount of H2S gas still present after the last stage from being released into the atmosphere as an emission, this largely inert lean gas is converted to SO2 in a post-combustion thermal process and afterwards often to sulphuric acid using a wet process.
The problem is the efficient oxidation of a large inert amount of waste gas, which has to be post-combusted safely with as less contactor fuel as possible, at low temperatures and with the shortest possible residence time. High calorific value process gas loaded with ammonia is often used as contactor fuel.
CS has developed its own waste gas incinerators for this application, which operate reliably at reaction temperatures of below 800°C. In order to be able to use fuels containing NH3 as well, part of the Claus waste gas is already supplied via the burner for flame cooling. Depending on the composition and process requirements, the remaining flue gas is injected into the combustion chamber in one or two stages via CFD-optimised gas injection systems. Swirl boosters in the burner chamber allow a further reduction in the size of the combustion chamber.
Backfire-safe exhaust gas combustion VARIEX
In many chemical or pharmaceutical production processes, gaseous by-products are produced. The composition as well as the amounts of these waste gases sometimes vary significantly as a result of production cycles.
The most common method for post-treatment of these production waste gases is combustion in special adiabatic combustion chambers with downstream waste heat utilisation. As some of these waste gases contain oxygen and are within the explosion limits, detonation safety devices or deflagration safety devices are mandatory in the burner chamber inlet. In many cases, a static flashback arrestor is provided in combination with a dynamic flashback arrestor. The dynamic backfire protection ensures that the minimum flow speed of the exhaust gas is always above the theoretically possible backfire speed. This is usually ensured by using nitrogen enrichment in the case of the often common fluctuations in the flow rate of the exhaust gas.
Even with minimum exhaust gas quantities, a high volume of inert nitrogen has to be added for heating in the combustion chamber. Therefore, CS has developed the patented VARIEX flue gas lance, which makes it possible to burn flue gas at a very high rate without adding nitrogen, even in existing incineration plants.
Savings in the six-digit euro range per year, as well as a CO2 reduction (through less fuel use), can be realised easily for operators and with low financial expenditure.
