Kraus process flow

Hello, our company can provide processes for handling sour gas across various ranges. We hope the moderator can provide some specific data so that our company can design a suitable process flow for you. Our company has extensive experience in acid gas recovery; if possible, you can contact us at 0510-80712168 (Engineer Zhao)

Then please also provide information on the air intake process at your factory, as different processes are required for acidic gases of varying concentrations; please be more specific

The industrial production of sulfur from acidic gases generally consists of two stages: a high-temperature thermal reaction in a sulfur production furnace and a low-temperature catalytic reaction in a converter. 1. High-temperature thermal reaction: Under high-temperature conditions in the sulfur production furnace, part of the acidic gases is first oxidized to SO2 by O2, while the remaining gases react with SO2 to form elemental sulfur. The main reactions are as follows: H2S + 3/2O2 = SO2 + H2O + 519.2 kJ (1); 2H2S + SO2 = 3/2S2 + 2H2O – 42.1 kJ (2). Under high-temperature conditions, these two reactions occur very rapidly, usually completing within 1 second, with a conversion rate of H2S of 60%–70%. 2. Low-temperature catalytic reaction: The low-temperature catalytic reaction takes place on the catalyst bed inside the converter, and the reaction equation is as follows: 2H2S + SO2 → 3/Sx + 2H2O + 93 kJ (3). Since this is an exothermic reaction, theoretically, the lower the reaction temperature, the higher the conversion rate. However, when the reaction temperature is below the sulfur dew point, a large amount of liquid sulfur deposits on the surface of the catalyst, causing it to lose its activity; therefore, the catalytic reaction temperature is generally maintained between 170 and 350 °C. With the improvement of sulfur production technology, catalytic reactions can also be carried out below the sulfur dew point, such as the CBA method and the MCRC method. The sulfur recovery rate for high-temperature thermal reactions and first-order catalytic reactions is generally between 75% and 90%. To improve this recovery rate, industrial practices often involve increasing the number of converters, installing condensers between them to separate liquid sulfur, and gradually reducing the temperature of the catalytic reactions. 1. 2 　Properties of sulfur: The element sulfur possesses a particular complexity; both its liquid and gas forms are mixtures of different sulfur compounds. Liquid sulfur is a mixture of S8 ring-shaped and Sn chain-shaped polymers, with the n value capable of reaching quite high values. Sulfur vapor is composed of eight components ranging from S1 to S8; at temperatures above 700 K, S2 is the predominant component in the gas, while below 700 K, S6 and S8 are the main components. In engineering, describing sulfur using the contents of the three components S2, S6, and S8 is sufficient to meet the design accuracy requirements. The reaction enthalpies for the conversions between various sulfur components are relatively large, as shown in chemical equations (4) to (6). 　　　3S2 S6 + 272.2 kJ (4) 　　　4S2 S8 + 404.4 kJ (5) 　　　4S6 3S8 + 124.5 kJ (6)

It was very helpful, thank you to the friend on floor 5

There is information on this topic in the forum; go and search, and you will find something useful.

Data on the composition and flow rate of acidic gases are required; in particular, the level of hydrogen sulfide determines which processing method should be used. Another one is the exhaust emission requirements.

:Lol 3.2 Main Process Features 3.2.1 The plant utilizes a two-stage conventional Claus process along with a direct-current sulfur recovery and purification system, ensuring a stable and high sulfur recovery rate. 3.2.2 Heating with saturated or superheated steam allows for the control of the inlet temperature of the reaction bed; this method is simple to operate, facilitates startup and temperature increase, aids in sulfur removal from the bed, and ensures high activity of the catalyst bed. 3.2.3 An H2S/SO2 ratio analyzer at the outlet of the final sulfur condenser is installed to achieve closed-loop control. Based on the H2S/SO2 ratio in the secondary Claus off-gases, the air volume in the air/acid gas control circuit is adjusted to achieve a H2S/SO2 ratio of 4:1 in the air, thereby ensuring a high sulfur recovery rate. 3.2.4 The reaction furnace is equipped with imported high-strength special burners, which also provides the system with greater operational flexibility. 3.2.5 The underground liquid sulfur storage tank is lined with acid-resistant and heat-resistant ceramic tiles; it features steam heating coils inside, as well as an external insulation layer with excellent thermal insulation and corrosion resistance properties, which helps to reduce heat loss and ensure long-term operation. 3.2.6 For the degassing of liquid sulfur, degassing equipment based on foreign MAG patents is used – this equipment offers simple operation controls and can reduce the amount of trace H2S dissolved in sulfur to below 10 ppm. 3.2.7 The reaction furnace is equipped with reliable igniters and flame detectors, and an optical thermometer is used to measure the temperature of the furnace in order to ensure the accuracy of temperature measurement. 3.2.8 Interlock protection is employed for the reaction furnace; multiple measurements are taken for key parameters such as furnace temperature, furnace pressure, the acid gas liquid separation tank, and the level of waste boiler liquid. Measures such as a two-out-of-three interlock system are used, which greatly enhances the reliability of the instruments and ensures the safe operation of the facility. 3.3 Main Feed Conditions 3.3.1 Operating Conditions for Acid Gas Feed Temperature: 30–55°C Pressure: 70–85 KPa (gauge pressure) Flow rate: 9000–30000 Nm3/h 3.3.2 Main Components of the Feed Acid Gas: Component (V)% Normal operating conditions Maximum operating conditions C1 0.22 0.21 CO2 34.43 32.28 H2S 58.39 60.52 COS 0.01 0.007 H2O 6.95 6.97 CH4S 0.004 0.004 Total flow rate (kmol/h): 1331.98 1660.77 3.3.3 Plant Yield Sulfur recovered by the plant: 23.75 t/h (depending on the properties of the feed gas) ； Yield: 93–95%; Factory yield: 99.8% 3.3.4 Material balance Material Name Weight percentage % Kilograms/hour Tonnes/day Tonnes/year Inlet Acidic gas 47.99 48,411 11,618.64 387,288 Combustion air 50.45 50,887 12,212.88 407,096 Deaeration air from liquid sulfur tank 0.84 849 20.376 6,792 Deaeration steam 0.72 726 17.424 5,808 Total 100 100,873 2,420.952 806,984 Outlet Sulfur product 23.75 23,592 566.208 188,736 Flue gas 76.25 75,730 1,817.52 605,840 Total 100 99,322 2,383.728 794,576 3.4 Process flow and principles 3.4.1 Brief description of the process flow The acidic gas coming from the natural gas desulfurization unit first enters the acid gas separation tank (111-D-301) to separate any condensate, thereby preventing it from reaching the burner in the reaction furnace (111-F-301) and causing issues with the unit operations and downstream equipment. The separated acidic condensate is sent to the acidic water stripping unit via the acid gas decanter bottom pump (111-P-302). The combustion air supply system, namely the Claus fans (111-K-301A/B), supplies the air required for combustion to both the reactor burner (111-F-301) and the hydrogen feed burner (111-F-401), while the combustion air needed for the flue gas incinerator is provided by the incinerator fans (111-K-401A/B) located near the incinerator. The amount of air supplied to the burner of the reaction furnace should be just sufficient to completely oxidize the hydrocarbons in the feed gas, while also meeting the air requirement for the partial combustion of H2S needed to maintain a H2S/SO2 ratio of 4:1 in the exhaust gases of the plant. Combustion reaction section: The equipment in the combustion reaction section includes the reactor burner (111-F-301), the reactor (111-F-302), the waste heat boiler (111-E-301/302), and the first-stage sulfur condenser (111-E-303). The most important parameters in the combustion reaction section are the reaction temperature, the degree of mixing of the reactants, and the residence time; appropriately increasing these three parameters can yield more ideal products from the combustion reaction. The temperature of the combustion reaction is approximately 1070°C. The main chemical reactions that occur in burners and reaction furnaces are: H2S + (3/2)O2 → SO2 + H2O (1); 2H2S + SO2 → SX + 2H2O (2). The combustion reactions in the reaction furnaces provide sufficient reaction time, while also enabling the effective removal of impurities present in acidic gases. The high-temperature process gas generated by combustion enters a waste heat boiler connected directly to the reaction furnace, where the waste heat is recovered by producing saturated steam at 3.5 Mpag pressure, thereby cooling the process gas to approximately 281°C. The cooled process gas enters the first-stage sulfur condenser, where it is further cooled to 172°C, resulting in the precipitation of liquid sulfur; at the same time, saturated steam at a pressure of 0.4 MPa is generated. The condensed liquid sulfur flows by gravity to the first-stage sulfur containment tank (111-S-302), and then to the liquid sulfur tank (111-S-301). In the catalytic reaction section, the process gas coming out of the first-stage sulfur condenser enters the first-stage reaction feed heater (111-E-304), where it is heated to 213°C by high-pressure steam at 3.5 MPag before entering the first-stage converter (111-R-301). Inside the reactor, the process gas comes into contact with the catalyst, and reaction (2) continues until equilibrium is reached. The sulfur produced during this reaction condenses as the process gas enters the second-stage sulfur condenser (111-E-305); it then flows through the second-stage sulfur storage tank (111-S-303) before reaching the liquid sulfur tank. The flow path of the process gas through the second-stage catalytic reaction section is the same as that in the first-stage catalytic reaction section; it is heated to 211°C in the second-stage reaction feed heater (111-E-306) before entering the second-stage converter (111-R-302). Within the second-stage converter, the process gas comes into contact with the catalyst and undergoes further reaction (2) until equilibrium is reached. The gas after the reaction enters the final sulfur condenser (111-E-307); the liquid sulfur that is condensed passes through the three-stage sulfur containment tank (111-S-304) before reaching the liquid sulfur tank. The exhaust gas exiting the final sulfur condenser goes on to the exhaust gas treatment unit. The liquid sulfur tank and the liquid sulfur degassing section: Liquid sulfur from various sulfur condensers flows by gravity to the liquid sulfur tank (111-S-301). There, the H2S content in the liquid sulfur can be reduced to below 10 ppm (w) using Black & Veatch’s patented MAG○R degassing process. The MAG○R liquid sulfur degassing process does not require the use of any chemical additives. Its principle of operation is as follows: liquid sulfur circulates in different sections of the liquid sulfur tank, and is mechanically agitated by primary and secondary injectors (111-EJ-302/303). The H2S dissolved in the liquid sulfur is released into the gas phase, and it is sent to the flue gas incinerator via exhaust pumps (111-EJ-301A/B) in order to keep the H2S concentration in the gas phase below its explosive limit. The liquid sulfur coming from the sulfur condensers at various stages generally contains 250–300 ppm (w) of H2S, depending on the operating conditions; the liquid sulfur condensed in the first-stage sulfur condenser, where the operating temperature is higher, has a higher H2S content than that condensed in the last-stage sulfur condenser, where the operating temperature is lower. In liquid sulfur, in addition to physical dissolution, H2S also exists in the form of polysulfides (H2SX). H2SX is a weakly bonded polysulfide formed through an equilibrium reaction between H2S and sulfur: H2S + (x-1)S → H2SX. Since an increase in temperature promotes this reaction to proceed in the right direction, the H2S content in the liquid sulfur condensed in the first-stage sulfur condenser is higher than that in the other sulfur condensers downstream. The degassed liquid sulfur overflows from the degassing area of the liquid sulfur tank to the storage area. A portion of this degassed liquid sulfur is pressurized by the liquid sulfur tank pumps (111-P-301A/B) and then sent to the sulfur cooler, where it is cooled to 138°C before being recycled back to the degassing area. The degassed liquid sulfur product is sent to the liquid sulfur forming unit via the liquid sulfur product pumps (111-P-303A/B) to produce granular solid sulfur, or to the liquid sulfur storage area. The boiler feedwater and steam system uses high-pressure deoxygenated water supplied from outside the plant. This water is heated by the boiler feedwater preheater E-308, and then its temperature is raised further by the final-stage sulfur cooler E-307 and the liquid sulfur cooler E-309, before it is used as feedwater for the waste heat boiler drum D-302. A small portion of the medium-pressure steam generated by the waste boiler is used as a heat source for the reheaters E-304 and E-306, while the remaining steam is superheated before being fed into the medium-pressure steam network. Low-pressure deoxygenated water from outside the unit is sent to each sulfur condenser (E-303, E-305), where it generates low-pressure steam that enters the low-pressure steam pipeline network. 3.4.2 Process Principle The sulfur recovery process using the Claus method involves two operating modes: the acidic gas operation mode (normal operation) and the fuel gas operation mode (heating operation). The reaction principle is as follows: 3.4.2.1 Acidic Gas Operation Mode (Normal Operation) The acidic gas operation mode corresponds to the normal operation of the plant. The acidic gas feed, mixed with an appropriate amount of air, enters the reactor (no fuel gas is required for combustion once the temperature is stable). This process relies on the incomplete combustion of H2S with oxygen (with a H2S/SO2 ratio of 4), with the aim of achieving a H2S/SO2 ratio of 4:1 in the Claus exhaust gases, thereby maximizing the conversion of H2S into sulfur. This process consists of four distinct conversion stages, namely: 1. Claus thermal conversion – the combustion reaction that takes place in the burner at the front end of the reactor, where all combustible components burn according to the following reaction. CH4 + 1.5 O2 → CO + 2H2O + 5538 kcal/Nm3
C2H6 + 2.5 O2 → 2CO + 3H2O + 9190 kcal/Nm3
H2 + 0.5 O2 → H2O + 2578 kcal/Nm3
All of these reactions proceed almost completely to the right, with a small amount of hydrocarbons being completely burned into H2O and CO2. The Claus reactions related to H2S in reaction furnaces are as follows: H2S → H2 + 0.5S2 – 905 kcal/Nm3 ① H2S + 1.5 O2 → H2O + SO2 + 5531 kcal/Nm3 ② H2S + 0.5 O2 → H2O + 0.5 S2 + 1674 kcal/Nm3 ③ The amount of H2S consumed in reaction ① accounts for approximately 6% of the H2S content in the feed acidic gas. The extent of thermal conversion reaction ③ is primarily determined by the H2S concentration in the feed acidic gas and the flame temperature that can be achieved through the combustion of part of the H2S; it is also influenced by the gas residence time within the thermal reactor. Furthermore, the thermal reaction zone also involves side reactions that produce COS and CS2; the formation of COS and CS2 is related to the concentration of CO2 and hydrocarbons in the acidic gases. 2. Claus catalytic conversion: The Claus catalytic reaction is an equilibrium reaction, and lower temperatures facilitate its occurrence. Under the action of an alumina catalyst, this process takes place in two steps: first, H2S and SO2 are converted at the optimal reactor inlet temperature, and then the sulfur produced as a result is condensed and separated. The main reactions are as follows: 2H2S + SO2 → 2H2O + 3/8 S8 + 557 kcal/Nm3; S8(g) → 4 S2(g) + 4327 kcal/Nm3; 3S8(g) → 4 S6(g) + 444 kcal/Nm3. The equilibrium reactions of gaseous sulfur are related to the combustion phase, the catalytic conversion phase, and the process gas cooling phase. In the first-stage Claus reactor, a side reaction occurs in which COS and CS2 are hydrolyzed to produce H2S; this reaction requires higher temperatures and can affect the overall degree of H2S conversion. The reactions are as follows: COS + H2O → H2S + CO2; CS2 + 2H2O → 2H2S + CO2. 3. Liquidification of the produced sulfur: The sulfur generated during the thermal conversion stage and the catalytic conversion stage is liquefied in a sulfur condenser. The main reactions are as follows: S8(g) → 8 S1(l) + 1117 kcal/Nm3; S6(g) → 6 S1(l) + 1171 kcal/Nm3; S2(g) → 2 S1(l) + 1372 kcal/Nm3. 4. Degassing of liquid sulfur: The sulfur produced by the sulfur recovery unit contains soluble H2S and H2Sx (polysulfides). The H2S present in the liquid sulfur can cause the H2S concentration in the sulfur shaping facilities and the liquid sulfur storage areas to exceed permissible levels. Therefore, it is necessary to degas liquid sulfur and reduce the H2S content to a safe level (below 10 mg/l). Liquid sulfur is cyclically degassed in dedicated degassing facilities for liquid sulfur, which accelerates the following conversion reactions of polysulfides, thereby achieving the purpose of degassing liquid sulfur. H2Sx → H2S + S (X-1) 3.4.2.2 Fuel gas operation scheme: 1. Claus unit – Before carrying out operations with acidic gases, the Claus unit must be heated up from a cold state; or, after operating with acidic gases, the sulfur accumulated in the Claus unit must be removed, and for this purpose fuel gas operations are required. During this mode of operation, it is necessary to keep the flame temperature below the maximum temperature of the reactor lining material; the flame temperature is adjusted to around 1250°C (not exceeding 1300°C) using quenching steam, which is injected into the burner and enters the acidic gas nozzles. When there is a small amount of sulfur present in the facility (sulfur generally appears on the catalyst bed in the Claus reactor during acid gas operations), the fuel gas must be burned in a stoichiometric manner. If the fuel gas is burned in the presence of excess oxygen, the free oxygen contained in the flue gases will react with the sulfur present in the facility, making it impossible to control the local temperature as well as the formation of SO2 and SO3. The reaction process is as follows: S + O2 → 2SO2 + 3165 kcal/Nm3. If there is a severe shortage of oxygen during the combustion of the fuel gas, the hydrocarbons contained in it cannot be completely burned, resulting in the formation of carbon. Carbon is adsorbed on the catalyst bed in the Claus reactor, causing the catalyst to become contaminated and its activity to decrease, as well as leading to a decline in sulfur quality and a reduction in conversion rates. When the oxygen deficiency during operation is no more than 5%, a portion of the methane contained in the fuel gas participates in the reaction according to the following equation: CH4 + 1.5 O2 → CO2 + 2H2O + 5538 kcal/Nm3. If there is a significant oxygen deficiency, methane burns according to the following reaction: CH4 + O2 → C + 2H2O + 4630 kcal/Nm3. In the same way, the reactions of hydrocarbons are more intense than those of CH4. Stoichiometric combustion refers to the complete combustion of all hydrocarbons present in the fuel gas into H2O and CO2; in such cases, there is little issue of excess or deficiency of oxygen in the flue gases (O2 below 0.4%, CO below 0.4%). During the combustion of fuel gas under stoichiometric conditions, the absolute flame temperature exceeds 1200°C; therefore, quenching steam must be used to regulate this temperature, and it is injected through the acidic gas nozzles of the main burner. The combustion reactions of the fuel gas components are as follows: H2 + 0.5 O2 → H2O + 2578 kcal/Nm3; CH4 + 2 O2 → CO2 + 2 H2O + 8560 kcal/Nm3; C2H6 + 3.5 O2 → 2 CO2 + 3 H2O + 15225 kcal/Nm3; C2H4 + 3 O2 → 2 CO2 + 2 H2O + 14170 kcal/Nm3; C3H8 + 5 O2 → 3 CO2 + 4 H2O + 21800 kcal/Nm3; C3H6 + 4.5 O2 → 3 CO2 + 3 H2O + 20600 kcal/Nm3; C4H10 + 6.5 O2 → 4 CO2 + 5 H2O + 28350 kcal/Nm3

If your company’s sulfur recovery capacity is no more than 20 tons per day, it is recommended to use the Lo-Cat process – it requires less investment, is simple to operate, can keep hydrogen sulfide levels in the exhaust gas below 1 PPM, and occupies less space. If you need consultation, contact me at 15958259291

I found the above posts very useful; thank you