Coke oven gas denitrification methods

Currently, the main processes are those for producing sulfuric acid and anhydrous ammonia.

Removal of ammonia 1.1 Ammonium sulfate process The process for producing ammonium sulfate is a traditional method for recovering ammonia from coke oven gas. Large and medium-sized coking plants built in China before the 1960s all used semi-direct saturators to produce ammonium sulfate; the main disadvantages of this process are severe equipment corrosion, poor quality of ammonium sulfate, and high resistance in the gas system. With the construction of Baosteel’s Phase I project, we introduced a process for producing ammonium sulfate using the pickling method. This process consists of three steps: pickling, vacuum evaporation and crystallization, followed by centrifugation, drying, and packaging of ammonium sulfate. Compared with the saturator method, by separating the ammonia absorption and ammonium sulfate crystallization operations, high-quality large-grained ammonium sulfate crystals can be obtained. The pickling tower is a air-sparging type tower, and the resistance in the gas system is only 1/4 of that in the saturator method, which allows for a significant reduction in the power consumption of the gas blower. A drying cooler is used to further cool the dried ammonium sulfate to prevent caking, which facilitates automatic packaging. The pickling process developed by our institute has also been successfully applied at Tianjin Gas Plant No. 2. With the construction of Xuansteel and Beijiao, we also introduced an ammonium sulfate production process using indirect saturators. This process recovers ammonia from acidic gases, and the quality of the product produced is better than that obtained using the saturator method. However, since it operates at relatively high temperatures (around 100°C), it requires high-quality materials for equipment and pipelines. Additionally, the size of the saturators is not smaller than that in the semi-direct method, so the investment required is higher than that for the semi-direct method. Ansteel No. 2 Recycling also introduced spray saturators from France to replace the saturators used in the semi-direct method. The spray-type saturator is characterized by low resistance in the gas system, reduced equipment size, and improved quality of ammonium sulfate. However, regardless of the process used for producing ammonium sulfate, from an economic perspective, its common fatal flaw is that the revenue generated from selling ammonium sulfate is far insufficient to cover its production costs. 1.2 Anhydrous ammonia process Another alternative method for ammonia removal is the production of anhydrous ammonia using the Fussam process. The Fussam process was developed by US Steel Corporation; it can absorb ammonia from coke oven gas (semi-direct method) or from acidic gases (indirect method). The second phase of Baosteel’s project utilized the Fussam unit, introduced from the American company USS, for the absorption of ammonia from coke oven gas. The coke oven gas was fed into the absorption tower, where gaseous ammonia came into direct contact with an ammonium phosphate solution; this process enabled the absorption of ammonia from the gas. Subsequently, through desorption and distillation, anhydrous ammonia was produced as the final product. This process makes use of the selective absorption property of ammonium dihydrogen phosphate to recover ammonia from gas, and then distills it to produce anhydrous ammonia with a purity of up to 99.98%. However, due to the corrosive nature of the medium, and the fact that desorption and distillation operations must be carried out at high pressures, high requirements are placed on the material used for the equipment. However, the economic viability of this process is greatly influenced by the production scale; when the scale is too small, it is neither economical nor easy to operate. While introducing the AS method for desulfurization, Pangang Coking Plant also installed an indirect Fussam method anhydrous ammonia plant; the acidic gases from the top of the acid removal tower were fed into the absorption tower of this indirect Fussam plant, where phosphoric acid solution was used to absorb the ammonia present in those acidic gases. Since it does not come into direct contact with gas, almost no acid tar is produced, allowing the treatment facilities for separating acid tar to be **simplified compared to the semi-direct method. Anhydrous ammonia produced by the Fussam process has high purity, a high value, and good economic benefits, but it is inconvenient to store and transport. 1.3 Ammonia decomposition process: A new process for catalytically decomposing ammonia was developed by the German company Steil. Since the decomposition of ammonia and hydrogen cyanide occurs through thermal cracking in a reducing atmosphere, it not only prevents hydrogen sulfide from participating in the reaction but also avoids the formation of NOx. The Shijiazhuang Coking Plant and the Tangshan Coking Plant have introduced this technology from the German company K.K. In this process, ammonia vapor containing a small amount of hydrogen sulfide is fed into an ammonia decomposition furnace via an AS cycle washing system; under the action of a nickel-based catalyst, NH3 and HCN are decomposed. The resulting decomposition gases are sent to a waste heat boiler to produce steam. After being cooled, these gases are further cooled by a second direct cooling system, and then mixed into coke oven gas with a calorific value of approximately 2900 kJ/m3. Our institute adopted a separate ammonia removal process in the design of Hansteel’s coking plant, where the ammonia vapor from water washing and steam ammonia treatment passes through a decompressor before entering the ammonia decomposition unit for decomposition. The process of catalytic ammonia decomposition has advantages such as being economical and practical, having low costs, allowing the exhaust gas to be mixed with coke oven gas, and producing no secondary pollution. As the products derived from ammonia production using coke oven gas become increasingly unprofitable, the aforementioned process deserves attention. 1. 4 Comparison of three ammonia recovery processes According to relevant reports, a comparative analysis of the above three types of ammonia recovery processes is conducted under the same basic parameters. The treatment capacity of the coke oven gas is 100,500 m3/h. The gas temperature is 25 ℃, and the gas pressure is around 14 kPa. The impurities in the gas are as follows: H2S at 8 g/m3, NH3 at 6 g/m3, HCN at 0.6–0.7 g/m3, and CO2 (by volume) at 2%. The amount of residual ammonia water is 55 m3/h. Analyzing this ammonia water shows that the free ammonia concentration is 3.5 g/L, fixed ammonium at 3 g/L, H2S at 0.3 g/L, CO2 at 2.5 g/L, and HCN at 0.2 g/L. In the purified gas, the concentrations are NH3 at 0.05 g/m3 and H2S at 0.5 g/m3. The ammonia content in the wastewater is 150 mg/L. All three processes involve the distillation of residual ammonia water. In the ammonium sulfide and anhydrous ammonia processes, final cooling of the gas before it enters the crude benzene absorption tower is also taken into account. Due to the high pressure loss in the saturator, the additional energy consumption of the blower is also included. The calculated values for the raw materials, energy consumption, and products of the three denitrification processes are shown in Table 1. Table 1 Raw materials, energy consumption, and products for the three denitration processes
Sulfur ammonium sulfate (semi-direct method) Fersam anhydrous ammonia (semi-direct method) Washed ammonia, steam-ammonia, and ammonia decomposition

Steam consumption, 0.2 MPa, t/h: 8 8 18
Steam consumption, 2.0 MPa, t/h: 1 11 –
Electricity consumption, kWh/h: 450* 240 90
Coke oven gas, m3/h: – – 900
Cooling water, m3/h: 970** 930** 660
100% sulfuric acid, t/h: 2.7 – –
100% NaOH, kg/h: 324 334 324
100% phosphoric acid, kg/h: – 7 –

Products
Anhydrous ammonia, t/h: – 0.93 –
Sulfur ammonium sulfate, t/h: 3.6 – –
2 MPa steam, t/h: – – 5.8
*Includes electricity consumption due to pressure loss of approximately 5000 Pa; **Includes water consumption for the final cooling of the gas. Table 2 Comparison of Operating Costs for Three Ammonia Removal Processes (10,000 yuan/year)
Item: Sulfuric ammonium, Anhydrous ammonia, Ammonia decomposition
Capital investment (10,000 yuan): 2230, 1860, 1500
Capital and maintenance costs: 220, 180, 150
Steam (net): 420.48, 946.08, 946.08, 641.23
Electricity: 157.68, 84.10, 31.54
Coke oven gas: –, –, 157.68
Cooling water: 339.9, 325.87, 231.26
Sulfuric acid: 2317.9, –, –
Alkali solution: 567.65, 585.17, 567.65
Phosphoric acid: –, 30.66, –
Total cost: 4023.61, 2151.88, 1779.36
Sulfuric ammonium: 3153.6, –, –
Anhydrous ammonia: –, 1385, –
Waste gas recovery: –, –, 210.94
Production cost: 870.01, 766.88, 1569.42
Cost per km3: 9.347, 8.239, 16.851
Based on the data in Table 1, the comparison of investment, maintenance, and operating costs for the three ammonia removal processes is shown in Table 2. As can be seen from Table 2, the ammonia washing system equipped with ammonia decomposition has lower capital investment and operating costs, but its production costs are high because the ammonia decomposition unit does not produce a commercial product.

The production process for liquid ammonia that we have developed does not require phosphoric acid; it involves low investment, low costs, and produces no wastewater.

The main problem is that, aside from the environmental requirement regarding ammonia, the amount of ammonia is very small (600,000 tons of compacted coke); obtaining liquid ammonia poses challenges in terms of handling it.

“The production process for liquid ammonia that we have developed does not require phosphoric acid; it involves low investment, low costs, and produces no wastewater. ”. For the fourth floor, could you briefly introduce the characteristics of your manufacturing process? This post was last edited by lucky1909 on 2009-3-28 09:42.]

Building on the existing ammonia vaporization process, by removing most of the carbon dioxide from ~18% concentrated ammonia solution, and utilizing principles of chemical engineering, a liquid ammonia production process is designed to convert most of the concentrated ammonia into liquid ammonia. The remaining small amount of ammonia solution is recycled rather than discharged; the residual liquid is sent back to the ammonia washing tower for reuse.

Currently, the main methods for gas ammonia removal in China include ammonia washing-ammonia decomposition, ammonium phosphate, sulfuric acid amine, and other methods. The option that offers good investment returns, simple operation, and excellent results is sulfuric acid AN. The main methods for producing sulfuric acid AN include the traditional saturator method, the pickling method (without a saturator), and the spray saturator method; the most modern approach is the spray saturator method. The traditional saturator method for producing ammonium sulfate involves gas passing through a distribution umbrella to bubble up through the mother liquor layer; as a result, there is high resistance in the gas system, the mother liquor contains high levels of acid tar, and the quality of the ammonium sulfate product is poor. This method has been gradually phased out. Ammonium sulfate is produced by the acid washing method, and the acid washing tower is a air-sparged tower; the resistance in the gas system is low. However, the fatal drawback of this method for producing ammonium sulfate is its long process flow, large land requirement, and high investment cost. The process of producing ammonium sulfate using the spray saturator method features low resistance in the gas system, larger crystal particles, high quality of ammonium sulfate, a short process flow, ease of operation, and a long service life for the equipment.

In terms of products, producing liquid ammonia is the best option; liquid ammonia has a wide range of applications and high added value, while other products have too low an added value. I have seen liquid ammonia production facilities of this kind.

There are several process methods for removing ammonia from gas: 1. Ammonia washing – ammonia distillation process to produce concentrated ammonia water; 2. Submerged saturator method for producing ammonium sulfate; 3. Sprayed saturator method for producing ammonium sulfate; 4. Acid scrubber tower method for producing ammonium sulfate; 5. Phosphoric acid absorption of ammonia to produce anhydrous ammonia; 6. Ammonia washing – ammonia distillation – ammonia decomposition process

The phosphoric acid deamination method is good; for steel complexes, concentrated ammonia can be used for desulfurization during sintering. This is an environmentally friendly approach these days, as it allows for the removal of ammonia from gas and sulfur from sintering flue gases, while also enabling the production of ammonium sulfate.