Energy-saving technical measures for the introduced equipment

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Energy-saving technical measures for introduced plants In recent years, large-scale ammonia synthesis plants in China have undergone extensive technological upgrades by adopting advanced international and domestic processes, equipment, and control technologies. Practice has shown that the following technologies are advanced, mature, and reliable, and can be chosen for use by enterprises during their upgrades. 　　Hydrocarbon steam conversion: Waste heat recovery from the flue gas in the first-stage furnace is utilized to reduce the temperature of the flue gases; rotary regenerative heat exchangers or heat pipe heat exchangers can be used to heat the combustion air ； By using a new catalyst and reducing the feed H2O/c ratio, not only is the steam consumption in the process reduced, but the thermal load associated with steam conversion in the first stage furnace can also be effectively lowered ； The use of conversion reactor tubes made from new alloy materials (such as HP50 thin-walled tubes) helps to increase the operating pressure and temperature of the conversion tubes, reduce the wall thickness and length of these tubes, and increase the amount of catalyst that can be loaded in them ； Modifying the steam system to increase the superheat of high-pressure steam can enhance the work capacity and thermal efficiency of the steam ； The two-stage furnace uses a new type of burner ； By drawing on the concepts of energy-efficient process design, the conversion process or the type of converter is modified to improve conversion efficiency and reduce energy consumption; the intensity of conversion in the first stage is decreased, allowing for a higher CH4 content at its outlet, while more air is introduced into the second-stage furnace to maintain the reaction temperature ； An air compressor is driven by a gas turbine, and the high-temperature air from the gas turbine is fed into the first furnace as make-up air; this combined cycle process allows for fuel savings and improved combustion efficiency in the first furnace. 　　Transformation: By using catalysts with a low water-to-carbon ratio and high activity, the CO conversion rate is increased while steam consumption is reduced. Reduce conversion resistance, such as changing the high-low conversion furnace from an axial bed to an axial-radial bed. 　　Decarbonization: Use low-energy-consuming decarbonization processes. Such as the low-heat-consumption phenol process (four-stage injection flash with semi-poor liquid), dual-tower regeneration process, MDIA process, etc. Through the adoption of a low-heat phenol process and associated modifications such as the replacement with high-efficiency stepped ring materials, the decarburization capacity has been increased by over 30%, while the heat consumption for regeneration has been reduced by 30%. 　　Ammonia synthesis and synthesis circuit: The use of new type internal components in the synthesis tower, along with small-particle, highly active catalysts, reduces the resistance in the synthesis tower and the synthesis circuit, increases the net ammonia yield, and enables better utilization of the heat generated during the synthesis reaction. The tower types currently used in large ammonia plants include the Casale type with axial radial cooling or interlayer heat exchange, the Topsoe S-200 type with radial interlayer heat exchange, and the Kelllogg horizontal synthesis tower – all of which have achieved good results. 　　Recovery of vent gas: Cryogenic separation or membrane separation techniques can be used; the latter is more commonly employed these days and yields excellent results. 　　Pump: A new type of efficient and energy-saving rotor designed using the “three-dimensional flow” concept ； Equipped with advanced anti-surge control systems and speed regulation systems ； Adopt state monitoring and fault diagnosis technologies for large-scale units ； Replacing some less efficient small steam turbines with motor drives helps improve the efficiency of the units and the reliability of the equipment operation. 　　Control System: The control system replaces traditional analog instruments with a computer-based distributed control system (DCS). By leveraging the extensive hardware and software capabilities of computers, it is possible to perform operations such as adjusting, indicating, setting, recording, alarming, and displaying dynamic charts for process variables. New progress has been made in the optimized control of key process parameters, intelligent start-up and shutdown control, advanced interlock control systems, as well as the integrated development of monitoring and control functions. These advancements contribute to the safe, stable, and optimized operation of the facility, resulting in significant energy savings. 　　Others: For the recovery of process condensate, medium-pressure steam (process steam) stripping or natural gas saturation methods can be employed ； Improve the structure of insulation materials and construction methods to reduce heat losses during the process and enhance thermal efficiency. For example, ceramic fiber felt insulation layers can be used in place of traditional refractory bricks. 　　 　　Slag-type units: The gasifier uses new types of burners, such as the multi-channel concentric circular burners found in shell gasification units; these burners can increase the effective gas content at the gasifier outlet by 4%, thereby reducing the consumption of ammonia and slag oil by nearly 40 kg/t ； The new burner developed by Texaco also reduces oxygen and steam consumption. The air separation unit adopts a full-low-pressure molecular sieve process to improve oxygen yield and reduce the power consumption of air compressors. The liquid nitrogen washing unit can employ the CO recovery technology using a shell cryogenic pump, or it can use the high-pressure expansion flash recovery technology designed by Linde Company, both of which can further reduce fuel consumption. The conversion process uses a wide-temperature, sulfur-resistant catalyst to increase the CO conversion rate. 2. Energy-saving technologies for large and medium-sized ammonia synthesis plants in China Enterprises that use natural gas as a raw material can employ heat-exchange conversion furnaces, which allow the natural gas consumption per ton of ammonia to be reduced to 750–800 Nm³ ； Pressurized gasification of crushed coal or pulverized coal to diversify raw material sources and improve carbon utilization efficiency to over 90% ； Optimize the batch gasification operation in a fixed-bed system at atmospheric pressure to achieve low consumption and high yield, with coal consumption per ton of ammonia being less than 1200 kg ； Constant-pressure oxygen-enriched continuous gasification technology for fixed-bed systems: improving the environment and reducing costs ； Full low-temperature conversion process: saves steam and increases plant capacity ； New decarbonization processes such as MID, MDHA, and dual-tower regeneration to reduce energy consumption ； New types of fillers, filters, etc., to improve efficiency ； Axial radial internals and low-temperature, high-activity catalysts to increase the capacity of the ammonia synthesis tower and its efficiency ； Hydrogen recovery technology via membrane separation or pressure swing adsorption ； Circulating fluidized bed boilers to improve the comprehensive utilization level of coal. 3. Energy-saving technologies for small-scale ammonia production 　Promote the use of low-temperature shift process technology, and phase out medium-temperature shift or medium-temperature with low-temperature combination technologies. This technology comes in two variants: full low-temperature shift and medium-low temperature shift, and can be chosen based on the specific conditions of each enterprise. Once implemented, the steam consumption in the shift system can be reduced to below 300 kg ； Polyethylene glycol dimethyl ether (NHD) or modified propylene carbonate decarboxylation technology is employed ； Iron-alkali solution catalytic gas desulfurization technology (DDs), a new desulfurization process by Keling ； The widespread adoption of optimized steam self-sufficiency technologies for ammonia synthesis, along with the development and use of centralized waste heat recovery units for upstream and downstream gas streams, D-type fans, and heavy-air combustion furnaces, has improved the technical level of the primary thermal network ； The success of the temperature-raising type one-in-one-out synthesis tower and the one-tower-one-pump conversion process has further optimized the process of the second thermal network ； Dual-tower parallel process for urea synthesis ； The adoption of the \"6-to-10\" and \"4-to-10\" technologies for small-scale urea production allows a urea production plant with a capacity of 40,000 tons per year to achieve a production rate of 320 tons per day (for a single urea tower) and 400 tons per day (for two urea towers). The ammonia consumption per ton of urea can be reduced to below 580 kg/t, while the steam consumption can be reduced to 1,000–1,200 kg/t ； Promote the retrofitting technology for gas generation furnaces, upgrading the original 2260 model to a 2610 model by adopting automatic coal feeding, new types of furnace grates, stepless speed control for the furnace strip mechanism, and D-type fans ； Promote the technology of vertical sieve plate towers ； Renovation of saturated hot water tower, carbonization to clear tower ； Promote new types of internal components for ammonia synthesis towers; the IIIJ-99 type, JR type, and NC type are recommended to increase the net ammonia yield and reduce the synthesis pressure ； Promote the use of fluidized-bed slag boilers that burn gas-generation slag with low calorific value; 1000 kg of steam can be produced as a by-product per ton of ammonia generated from such slag ； Synthetic ammonia-urea steam self-sufficiency technology ； High-pressure loop stripping technology for full-cycle urea plants ； Implement an gas generation and blowing air recovery system ； Computer-optimized control of conversion systems and ammonia synthesis systems ； Optimize the pressure of the helium synthesis system to achieve low-pressure synthesis, thereby significantly reducing the power consumption of the product ； Promote computer-based distributed control systems to ensure stable and safe production of equipment. Caustic soda products 　① Adopt expanded anode and modified diaphragm technologies to promote energy-saving diaphragm electrolyzers ； ②Use large thyristor rectifier units to improve rectification efficiency ； ③Improve the quality of brine to optimize and automate the caustic soda production process. In the production process using the ion exchange membrane method, a secondary brine purification step is included, ensuring the quality of the brine. However, in the production of caustic soda via the diaphragm process, there is a common issue related to improving the quality of the brine. Along with technological upgrades to the electrolysis process for caustic soda production using this method, it is necessary to reduce the levels of calcium and magnesium impurities in the brine from 10 ppm (1 ppm = 10⁻⁶) to below 5 ppm, as well as to keep the level of insoluble substances below 3 ppm. Techniques such as the use of acidic brine should be employed, along with microcomputer-controlled systems for managing the production process, in order to further reduce energy consumption ； ④Promote the three-effect counter-current partial forced-circulation evaporation process, upgrade the evaporation equipment to reduce steam consumption, and use large chlorine turbines to replace Naismith pumps for transporting chlorine, achieving significant energy savings ； ⑤The ion-exchange membrane process for producing caustic soda is the preferred technology for developing caustic soda production and replacing graphite anode membrane processes; its superiority is recognized worldwide, and it represents an effective measure for saving energy in caustic soda production. 　　Soda ash: Vigorously promote the 22 energy-saving and consumption-reducing technical measures that have been proven to be effective and mature, which are classified into the following categories: ① Cogeneration, multi-stage steam utilization technology ； ②Technologies for improving local processes: washing water additive technology for vacuum caustic soda machines, vacuum distillation technology in ammonia-alkali process plants, dry ash addition technology in ammonia-alkali process plants, direct production of caustic soda from synthetic ammonia shift gas (Soda Ash Process), liquid ammonia cooling and full-level control technology for external coolers in the Soda Ash Process, steam recovery technology through flash evaporation of waste liquids from ammonia-alkali distillation, recycling technology for ammonia water in Soda Ash Process plants, reverse material removal technology, and secondary filtration technology for heavy caustic soda, etc ； ③Highly efficient and energy-saving equipment is used, including naturally circulating externally cooled carbonization towers (for caustic soda production), new types of steam burners with self-regulating alkali return, internally cooled absorption towers, rotary alkali cooling furnaces, and new types of heat exchange equipment ； Such as bellows heat exchangers, plate heat exchangers, and new types of bubbling beds for heavy alkalis that combine drying, cooling, and grading functions ； ④Automated detection and control methods are employed to further optimize the process conditions and reduce the mother liquor circulation equivalent, thereby achieving energy savings. 　　Calcium carbide production: In China, large and medium-sized calcium carbide furnaces with a capacity of over 10,000 kVA account for about one-third of the total production capacity; there are also a considerable number of small furnaces and open-type furnaces. Calcium carbide furnaces can be roughly classified into closed furnaces, semi-closed furnaces, and open furnaces, with significant differences in the technical and equipment standards among these different types of furnaces. 　　1. Promoting advanced technical equipment 　Promote the use of advanced technical devices, such as the sealing of calcium carbide furnaces and the design of their covers, the selection of structural and electrical parameters for these furnaces, the design of gripper components, systems for recovering furnace gases or other forms of thermal energy, systems for utilizing pulverized coal and ash, mechanization for removing calcium carbide from the furnaces, automatic control systems, energy-saving transformers and designs for energy-efficient electrical systems, as well as comprehensive facilities for environmental protection, occupational safety, and industrial hygiene. 　　2. Furnace gas purification technologies and utilization methods The utilization of calcium carbide furnace gas is an important issue, as it allows for the recovery of energy while reducing air pollution. Abroad, it is used as fuel for lime kilns after dust removal to clean the furnace gas, but it has not yet been fully utilized in China. There are two methods for extracting clean furnace gas, both domestically and internationally: the wet method and the dry method. The wet method requires less investment, but there is secondary pollution from wastewater ； Dry processing involves high investment, but there is no issue of secondary pollution. 　　The dry dust removal technologies introduced from Japan’s Diamond Company and Norway’s Aker Company in our country have proven to be unreliable, whereas the wet dust removal technology introduced, despite its shortcomings, can still operate continuously. Both the domestically developed boiler system for direct combustion of gas from closed calcium carbide furnaces, and the semi-closed furnace flue gas waste heat boiler system, belong to the dry-type category; heat exchange and dust removal take place simultaneously. These systems have achieved certain energy-saving results in actual production, and the dust content in the exhaust gases meets the regional emission standards. The dry-process technology developed domestically is only suitable for factories that require steam. For enterprises producing calcium carbide for commercial use, it is necessary to study and improve China’s wet-process technology, as well as work on implementing a closed-loop system for wastewater treatment. This approach not only allows for significant water savings but also minimizes secondary pollution. 　　3. Directions for technical upgrading of large and medium-sized calcium carbide furnaces: Enclosed furnaces provide the necessary conditions for ensuring occupational safety and industrial hygiene, while semi-enclosed furnaces are superior to open furnaces in terms of dust removal. The direction for technological improvement is toward encapsulation; enclosed furnaces can utilize hollow electrode systems to recycle the powder material and fully recover the thermal energy from the furnace gases. 　　Medium and large-scale calcium carbide furnaces should be equipped with microcomputer control ； A mechanized automatic feeding and batching system with a sealed design, connected to a microcomputer for interlock control, not only improves work efficiency and reduces dust generation but also ensures accurate mixing ratios ； Design of energy-efficient transformers and other systems for saving electrical power. 　　In the technical equipment for calcium carbide furnaces in our country, there is no economically viable mechanized equipment for removing the product from the furnace; this not only hinders the smooth extraction of calcium carbide and leads to energy waste, but also makes it difficult to avoid accidents during this process. The 45,000 t/year fully enclosed calcium carbide furnace introduced from Aker Group in Norway in the 1980s features three symmetrically arranged single-phase energy-saving transformers to minimize the length of the electrical circuits. It is equipped with a microcomputer control system and a hollow electrode system, enabling continuous and automated, sealed batching and discharging processes. Additionally, it has a dry purification system for removing dust from the furnace gases. 4. Energy-saving technologies, equipment, and designs to be promoted prioritarily 　　① Waste heat boilers 　　China is a major producer of calcium carbide; in the 1980s, there were over 400 calcium carbide production enterprises with more than 500 furnaces. Through practical production experiences, many useful technologies and production techniques have been developed for various types of furnaces. Boilers that utilize direct combustion of furnace gas, as well as waste heat boilers for flue gas, are examples of successfully designed thermal energy recovery systems. Promote the direct combustion of furnace gas in closed furnaces in factories that require steam, yielding 1.3–1.5 tons of steam per ton of calcium carbide produced ； A semi-hermetical furnace flue gas waste heat boiler can produce 0.8–1.0 tons of steam per ton of calcium carbide produced. 　　Plans are in place to have medium and large-scale calcium carbide manufacturers design dual-fuel (coal and calcium carbide furnace gas) boilers for self-power generation; the dual-fuel boiler approach using furnace gas as an auxiliary fuel source is feasible. If calcium carbide manufacturers utilize calcium carbide furnace gas for self-power generation, it can reduce reliance on grid electricity if successful. 　　②Hollow electrodes: China has introduced multiple sets of production technologies for hollow electrodes, including those from Germany, Japan, and Norway. Powdered coal and powdered ash, in a total proportion of 8%–15%, can be added to the hollow electrodes to achieve energy savings and material conservation across the entire system. 　　③Microcomputer control: Promoting the use of microcomputer control helps to achieve stable and efficient production. The microcomputer control software and hardware developed in China have proven to be effective through practical production use. 　　④Others 　In addition to energy savings through process design, energy conservation in electrical systems is also very important, including the use of energy-efficient transformers and optimized design of power distribution networks. 　　Yellow phosphorus products: Large electric furnaces with a production capacity of over 7,000 tons per year ； For electric furnaces with a capacity of over 30,000 tons per year, the power consumption should be below 14,000 kWh/ton ； Eliminate small electric furnaces with a production capacity of 2,000 t/year or less ； Adopt a refined feed policy to improve the quality of phosphate ore fed into the furnace and reduce power consumption ；