Innovative Wet Desulfurization Equipment (Precise Hydrogen Sulfide Control for Cleaner Air)

Shanxi Fenxi Machinery and Electronics Co.,Ltd 
Desulfurization Treatment of Qingxu Landfill Project Case Study

Currently, there are two main types of desulfurization processes used domestically for biogas: dry desulfurization and wet desulfurization. Dry desulfurization can be further classified into iron oxide desulfurization and activated carbon desulfurization. Both of these dry desulfurization methods have common drawbacks, including a low sulfur capacity of the desulfurizing agent, limited flexibility in operational load, and difficulties in desulfurizing agent regeneration. These drawbacks are mainly manifested in:

(1) If the H₂S content in biogas is high, the desulfurizing agent quickly loses effectiveness, resulting in a sharp decrease in desulfurization efficiency, which in turn affects the quality of ceramic products.

(2) In terms of regeneration, the regeneration of activated carbon requires superheated steam with a temperature greater than 400°C. However, this type of steam is not only difficult to obtain, but also when the desulfurization tower has a large diameter or a high bed depth, complete regeneration is practically impossible. As a result, many users have to use expensive activated carbon desulfurizing agents as disposable materials. On the other hand, the regeneration of iron oxide requires oxygen from the air. It is well known that if a suitable amount of air is mixed into biogas, it can cause explosions. Therefore, the regeneration of iron oxide must be carefully conducted, and any negligence by the operators is not allowed. Additionally, the regeneration process should be extremely slow to prevent the spontaneous combustion of sulfur due to accelerated reactions. The regeneration cycle of iron oxide is relatively short, which increases the labor intensity for workers.

(3) The main focus is on the dry desulfurization process, and if the design specifications are determined, adjustments may not be possible. For example, if the design desulfurization target specifies that the H₂S content in the biogas after desulfurization should be 50mg/Nm³, the initial biogas quality may meet the standard. However, it will soon be observed that the H₂S content in the biogas keeps increasing, eventually affecting the quality of ceramic products, indicating the failure of the desulfurizing agent and requiring regeneration. Each regeneration of the desulfurizing agent significantly reduces its desulfurization effectiveness. Considering the drawbacks of dry desulfurization mentioned above, our company took the lead in adopting wet desulfurization for biogas applications. Compared to dry desulfurization, wet desulfurization offers simpler regeneration (regeneration can be carried out while the system is operating), easier operation, stable desulfurization targets (only a small amount of desulfurizing agent needs to be added to the desulfurization solution per shift to meet the desired desulfurization target), flexibility in operation (desulfurization targets can be controlled by adjusting the dosage of the desulfurizing agent), and better desulfurization effectiveness (achieving an H₂S content in the biogas of less than 20mg/Nm³). This method meets the requirements of gas power generation technology and enables your company's power generation units to meet national environmental emission standards.

Our company applies the CoS method in wet desulfurization. Compared to other methods, the CoS method offers stable operation, high desulfurization efficiency, and low raw material consumption.

In recent years, with the rapid development of science and technology, the upgrading of desulphurization agent is fast, and our company has made significant development in the field of desulphurization, CoS series of new high-efficiency desulphurization catalyst is the high-tech achievements developed by our company to meet the current market demand, and its technical performance has reached the international advanced level. Based on extensive research into the desulphurisation agent market, we have analysed in detail the advantages and disadvantages of various desulphurisation agents at home and abroad. Through extensive consultation with users, and according to the actual use of each plant and the changes in the level of sulphur content in the gas, we have continuously improved the product formula and the use of technology. The new CoS high-efficiency desulphurisation catalyst was developed comprehensively, which has the outstanding advantages of low consumption and low cost. CoS high-efficiency desulphurisation catalyst is a double-controlled metal phthalocyanine cobalt compound, which is an ultra-high activity desulphurisation catalyst. It is mainly used in liquid-phase catalytic oxidation desulphurisation and decyanidation, its desulphurisation efficiency reaches more than 99% and decyanidation efficiency reaches more than 98%. At the same time, it can also remove more than 60% of organic sulphur, and the units using it have achieved good technical results with significant economic and social benefits. The CoS high efficiency desulphurisation catalyst is a new generation of desulphurisation catalyst developed by further improving the active components and optimising the production process. Compared with the prototype catalyst, CoS high efficiency desulphurisation catalyst has the advantages of easy production and operation, high desulphurisation efficiency, high sulphur capacity, good selectivity, clear regeneration solution, no tower blocking, easy sulphur separation, low consumption and low cost, etc. It is the high efficiency catalyst of choice for desulphurisation in fertiliser and coking enterprises.

1. Physical and Chemical Properties:
Appearance: Bluish-gray powder.
Density: ≤0.96 g/cm³
Main component: >92%
Insoluble in water: ≤3.0%. It has good solubility in water or alkaline solutions.
 In pure alkaline solutions, it appears sky blue, and in ammonia solutions, it appears light green.
It does not decompose in acidic or alkaline media and exhibits good chemical stability.
The catalyst itself is non-corrosive and non-toxic.

2. Applications and Features:
CoS desulfurization catalyst can be widely used in the gas-phase wet oxidation desulfurization process of various types of biogas, generator gas, and city gas. The product is non-toxic, non-corrosive, and non-polluting. Under normal or pressurized conditions, whether using ammonia water or caustic soda as the absorbent, it can maintain a stable desulfurization efficiency. The product does not require the addition of auxiliary catalysts during use. The pre-activation process is simple and short, and the hydrogen sulfide removal rate can reach over 99%, the organic sulfur removal rate can reach over 60%, and the hydrogen cyanide removal rate can reach over 98%.The product has high activity, long lifespan, and strong resistance to hydrogen cyanide poisoning. It can dissolve and remove deposited and adhered sulfur in the desulfurization system, thereby cleaning the system equipment. The product has a high sulfur capacity, good regeneration, large suspended sulfur particles, which are conducive to separation, does not block the tower, and achieves high purity of removed sulfur, without corroding the equipment. It does not accumulate in the desulfurization device, has no liquid waste disposal issues, does not cause environmental pollution, reduces system resistance during use, reduces energy consumption, extends equipment maintenance periods, and significantly reduces desulfurization costs. The process of using this product is simple, does not change the original process flow, does not require additional equipment, and is convenient to replace traditional desulfurizing agents.

3. Chemical Reaction in the Desulfurization Process (Sodium-based example):
The chemical absorption reaction when get rid of H₂S
_{H2S+Na2CO3=NaHS+NaHCO3
NaHS+(x-1)S+NaHCO3=Na2Sx+CO2+H2O}

The catalytic oxidation reaction of segregation sulphur
2NaHS+O2CoS2NaOH+2S ↓
Na2Sx+H2O+1/2O2CoS2NaOH+Sx ↓

The chemical absorption reaction when get rid of organic sulphur
CoS+2Na2CO3+H2O=Na2CO3S+2NaHCO3
RSH+Na2CO3=RSNa+NaHCO3

The catalytic oxidation reaction of organic sulfide
2Na2CO2S+O2CoS2Na2CO3+2S ↓
4RSNa+O2+2H2OCoS2RSSR+4NaOH

4. Instructions for Use:
In the application of the liquid-phase catalytic method for desulfurization of sulfur-containing gases, the following instructions should be followed:

(1) Preparation:
Prepare a small solution bucket with a welded drain pipe and valves, with a capacity of 50-150 liters. Fill the bucket with water, ammonia water, alkaline solution, or desulfurization solution. Calculate the catalyst dosage based on the desulfurization quantity of the factory, with an initial dosage of around 20-30PPM. After adding the catalyst, use compressed air to agitate or stir several times with a wooden stick to dissolve the catalyst. Then activate it for 4 hours, stirring once every hour during this period to ensure full activation. It should be noted that if the activated liquid is white, it should not be used. If it is green or if the dissolved water is sky blue, it can be used.

(2) Method of Introduction
Slowly and evenly add the activated catalyst solution into the lean liquid tank or liquid conditioner. Do not add it onto the sulfur foam layer to prevent loss of the effective components of the catalyst along with the foam. After the activated catalyst solution enters the system, a large amount of sulfur foam will appear after 3 hours. It is necessary to strengthen the removal of the sulfur foam, and the desulfurization will return to normal after 1-2 days.

 As the deposited sulfur and adhered sulfur are removed, there may be an increase in suspended sulfur in the solution. Sometimes, there may be slight fluctuations in H₂S after desulfurization. In such cases, the air supply can be increased. As the operating time increases, the removal of system sulfur foam gradually returns to normal.

(3) Method of Replenishment
The composition of the desulfurization solution and the required amount of catalyst replenishment should be determined based on the operating conditions of the system. To determine the optimal replenishment amount, it is generally estimated that around 1.5g of CoS is needed to remove 1kg of H₂S.

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