Sulfur Daily Question, May 4th------3 points for participation, 10 points for a correct answer

The types and concentrations of impurities in acidic gas are highly dependent on its source, mainly including CO2, hydrocarbons, H2O, and NH3. Carbon dioxide and hydrocarbons are carbon-based pollutants; their main hazard is the formation of carbonyl sulfide and carbon disulfide within the main furnace (due to temperature control), and some of those that do not burn completely will cause carbon deposition in the bed layer ； Water itself does not enter the reaction furnace (separation occurs beforehand), and the reaction itself generates a certain amount of water. However, in case of abnormal conditions, the entry of water vapor into the combustion furnace will significantly lower the temperature; the accumulation of large amounts of water vapor will increase the pressure in the furnace, damaging its refractory structure. If the main reactor vessel ruptures and water gets in, it will cause hydrothermal aging of the catalyst, shortening its lifespan. If ammonia is not burned in the combustion furnace, it will later cause catalyst poisoning and the formation of crystalline amine salts that lead to blockages (in the quench tower section). All inert gases (carbon dioxide can also be considered to some extent) increase the load on the equipment (thermal load), reduce the sulfur recovery rate, and raise the cost of equipment investment.

When the hydrocarbon content in acidic gases exceeds the limit, incomplete combustion leads to the formation of carbon black, causing issues such as catalyst deactivation and pipeline blockages.

This post was last edited by Zhongyuanren on 2016-5-4 at 16:59. The hazards of hydrocarbons: When the levels of hydrocarbons and other organic substances are high, it not only raises the temperature of the combustion furnace but also increases the thermal stress and heat load on the waste heat boiler. It also increases the amount of air required for combustion. The CO2 and H2O produced as a result of combustion act as inert gases that dilute the reactants, thereby suppressing the Claus reaction. When the hydrocarbon content fluctuates greatly, it can lead to uneven air distribution during combustion. On one hand, this may result in oxygen leakage; on the other hand, heavier hydrocarbons, especially aromatics and alkylol amines, will decompose under conditions of low oxygen availability, producing carbon deposits that contaminate sulfur products, clog catalysts, and render them inactive. Therefore, the hydrocarbon content in acidic gases is generally required to be <2%. Effect of CO2: In most cases, H2S and CO2 together constitute the main components of acidic gases. In addition to its diluting effect, the CO2 in acidic gases has the main harmful effects of lowering the flame temperature in the reaction furnace and increasing the levels of COS and CS2 in the process gas at the outlet of the combustion furnace; if it is not sufficiently hydrolyzed during the low-temperature catalytic reaction stage, this will affect the conversion rate and yield of the facility. The formation of COS and CS2 is related to the CO2 concentration and hydrocarbon content in the acidic gas. Effect of HO2: The impact of water vapor on the operation is not as significant as that of NH3 and CO2, but it is still considerable. It acts as an actual inert substance as well as a product of the Claus reaction; therefore, it affects both the Claus equilibrium and the effective partial pressures of the reactants.

If acidic gases contain hydrocarbons (amines), the lack of sufficient air will lead to severe carbon deposition of these hydrocarbons (amines); especially amines, which form shiny tar-like deposits. This increases the coking load during sulfur unit shutdowns, prolonging the downtime. More importantly, an excessive amount of carbon buildup can cause the device to become blocked under normal operation, leading to the rupture of the explosion-proof membrane and subsequent leakage of toxic gases.

It will reduce the hydrogen sulfide partial pressure, which is unfavorable for the progress of the reaction and thus leads to a decrease in conversion rate

What are the effects of acidic gas impurities on the sulfur recovery unit? Answer: Impurities in the acidic gas fed into the system include (1) hydrocarbons and alcoholamine solvents. When the concentration of these substances is high, they not only cause the temperature of the combustion furnace to rise and increase thermal stress and heat load in the boiler, but they also increase the amount of air required for combustion. The CO2 and H2O produced as a result of combustion act as inert gases that dilute the reactants, thereby suppressing the Claus reaction. An excessive amount of hydrocarbons increases the production of COS and CS2 in the reaction furnace, affecting the sulfur conversion rate. When the hydrocarbon content fluctuates significantly, it can lead to uneven air distribution during combustion. On one hand, this may result in oxygen leakage; on the other hand, heavier hydrocarbons, especially aromatics and alkyl alcohol amines, will decompose under conditions of low oxygen availability, producing carbon deposits that contaminate sulfur products, clog the catalyst beds, and cause them to become inactive. This leads to an increase in system pressure, and in severe cases, the plant is forced to shut down. Therefore, the hydrocarbon content in acidic gases is generally required to be <3%. (2) Ammonia: Ammonia in the feed gas is another common issue in sulfur recovery units; generally, the ammonia content in the feed gas should not exceed 3%. The impact of ammonia present in the feed gas on the proper operation of sulfur recovery units cannot be underestimated; this is manifested in the fact that, before the acidic gas enters the furnace, various ammonium salts can clog the equipment and pipelines, thereby affecting the normal transfer of the acidic gas. After entering the system, the nitrogen and water generated by the combustion of ammonia are inert components in the Claus reaction; they reduce the sulfur partial pressure, thereby lowering the sulfur yield. Incomplete combustion of ammonia reacts with acidic components in the process gas to form ammonium hydrosulfide or ammonium polysulfide crystals, which can block the tubes of the condenser, increase the system pressure drop, and even force the plant to shut down. The reaction between ammonia and alumina leads to catalyst deactivation, and its by-product, nitrogen oxides, cause environmental pollution. Moreover, nitrogen oxides act as a catalyst for the further oxidation of sulfur dioxide, resulting in sulfuric acid corrosion, which in turn causes equipment corrosion and catalyst poisoning. (3) CO2: In most cases, H2S and CO2 together constitute the main components of acidic gases. In addition to its diluting effect, the CO2 in acidic gases has the main harmful effects of lowering the flame temperature in the reaction furnace and increasing the levels of COS and CS2 in the process gas at the outlet of the combustion furnace; if it is not sufficiently hydrolyzed during the low-temperature catalytic reaction stage, this will affect the conversion rate and yield of the facility. (4) Water: As a practical inert substance and also a product of the Claus reaction, water affects both the Claus equilibrium and the effective partial pressures of the reactants, thereby reducing the conversion rate of hydrogen sulfide and the yield of sulfur. The water vapor content in typical acidic gases is about 2% to 5%.

The impact of acidic gas impurities on the sulfur recovery unit (1) Hydrocarbons and alcohol amine solvents: When their concentrations are high, they mainly cause an increase in the temperature of the combustion furnace, as well as increased thermal stress and heat load on the boiler. They also increase the amount of air required for combustion. The CO2 and H2O produced by this combustion act as inert gases that dilute the reactants, thereby suppressing the Claus reaction. An excessive amount of hydrocarbons increases the production of COS and CS2 in the reaction furnace, affecting the sulfur conversion rate. When the hydrocarbon content fluctuates significantly, it can lead to uneven air distribution during combustion. On one hand, this may result in oxygen leakage; on the other hand, heavier hydrocarbons, especially aromatics and alkyl alcohol amines, will decompose under conditions of low oxygen availability, producing carbon deposits that contaminate sulfur products, clog the catalyst beds, and cause them to become inactive. This leads to an increase in system pressure, and in severe cases, the plant is forced to shut down. Therefore, the hydrocarbon content in acidic gases is generally required to be <3%. (2) Ammonia: Ammonia in the feed gas is another common issue in sulfur recovery units; generally, the ammonia content in the feed gas should not exceed 3%. The impact of ammonia present in the feed gas on the proper operation of sulfur recovery units cannot be underestimated; this is manifested in the fact that, before the acidic gas enters the furnace, various ammonium salts can clog the equipment and pipelines, thereby affecting the normal transfer of the acidic gas. After entering the system, the nitrogen and water generated by the combustion of ammonia are inert components in the Claus reaction; they reduce the sulfur partial pressure, thereby lowering the sulfur yield. Incomplete combustion of ammonia reacts with acidic components in the process gas to form ammonium hydrosulfide or ammonium polysulfide crystals, which can block the tubes of the condenser, increase the system pressure drop, and even force the plant to shut down. The reaction between ammonia and alumina leads to catalyst deactivation, and its by-product, nitrogen oxides, cause environmental pollution. Moreover, nitrogen oxides act as a catalyst for the further oxidation of sulfur dioxide, resulting in sulfuric acid corrosion, which in turn causes equipment corrosion and catalyst poisoning. (3) CO2: In most cases, H2S and CO2 together constitute the main components of acidic gases. In addition to its diluting effect, the CO2 in acidic gases has the main harmful effects of lowering the flame temperature in the reaction furnace and increasing the levels of COS and CS2 in the process gas at the outlet of the combustion furnace; if it is not sufficiently hydrolyzed during the low-temperature catalytic reaction stage, this will affect the conversion rate and yield of the facility. (4) Water: As a practical inert substance and also a product of the Claus reaction, water affects both the Claus equilibrium and the effective partial pressures of the reactants, thereby reducing the conversion rate of hydrogen sulfide and the yield of sulfur. The water vapor content in typical acidic gases is about 2% to 5%.

It causes catalyst deactivation, pipeline blockages, etc., affecting sulfur recovery rates

It can easily cause fluctuations in furnace temperature, affecting both the furnace temperature and system pressure; it also tends to produce black sulfur, which leads to catalyst deactivation. I don’t know about the others.

Raising the operating temperature of the main combustion furnace may affect its long-term safe operation; it reduces the sulfur recovery rate of the sulfur recovery unit; it increases air consumption; it affects the quality of sulfur; and it increases energy consumption.