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A Brief Discussion on the Alcohol-Ammonia Production Process Using Coal as Raw Material by Zhou Daming, Shandong Mingshui Dahuagroup, December 22, 2008. The basic energy situation in China is characterized by a lack of oil and gas, but an abundance of coal. With the rapid development of the national economy, alternative energy sources to oil have received increasing attention; from technical, economic, and environmental perspectives, methanol appears to be the most viable option as a substitute for oil. The recent activity in the methanol market also objectively confirms this reality. The use of coal as a raw material in fixed-bed batch gasification processes for the co-production of nitrogen fertilizers and methanol remains an important method for methanol production at present. This is a reality dictated by China’s actual national conditions, and due to various constraints, it is not possible to change this situation fundamentally in the short term. Fixed-bed batch gasification using coal as raw material, represented by gas generators of the Ф2600 series, makes extensive use of technologies such as pulverized coal briquette gasification, slag recycling, and heat and power generation from blast air recovery. These technologies greatly improve the utilization rate of the calorific value of the raw coal, allowing the gas generation capacity of the gas generators to be fully utilized. This is an important factor that enables small and medium-sized nitrogen fertilizer plants, along with their Ф2600 series gas generators, to survive and develop in the highly competitive economic environment. The synthetic ammonia and glycol process is an important technological upgrade developed in response to the economic demands of the nitrogen fertilizer and methanol industries, and it still possesses significant advantages for further development. The hydroformylation process plays an important role in reducing the cost of ammonia synthesis, increasing production, and developing methanol production; it is a technical improvement project that requires low investment, yields quick results, and offers high returns. The ligand alcohol process requires that the alcohol-to-ammonia ratio be maintained within an appropriate range; if this ratio is too high, gas consumption and operating costs increase. In today’s environment of rapid growth in the methanol market, many nitrogen fertilizer manufacturers are turning their attention to alcohol-ammonia technology for technological upgrades, and the technological transformation using alcohol-ammonia technology is currently in progress at Mingshui Fertilizer Factory. 1. Alcohol amine production process: The so-called alcohol amine process makes use of the existing infrastructure in nitrogen fertilizer plants and fixed-bed gas furnaces to produce water gas, N2-rich gas, and methanol synthesis off-gases that meet the requirements for methanol synthesis; these gases are then recycled into the ammonia synthesis system. This includes hydrogen recovery from decarburization off-gases, thereby minimizing the loss of useful gases during the methanol production process, which highlights the advantages of this approach in nitrogen fertilizer production. The alcohol-to-ammonia ratio in the alcohol hydrazine process is clearly much higher than that in the diol process. The alcohol hydrazine process is shown in the figure: ① Gas generation is carried out using an existing gas furnace; the process pipelines need to be modified, and a water-gas holder must be installed separately ； ②For water gas desulfurization, wet desulfurization is selected depending on the H2S content level ； ③The compressor uses four-stage compression; a reciprocating compressor is suitable, and it can be driven by an electric motor or by steam ； ④The transformation employs a full-low-temperature serial medium-temperature hydrolysis process for the conversion of organic sulfur ； ⑤Wet method is suitable for desulfurizing the transformed gas; the H2S content after desulfurization depends on the requirements of the decarburization method ； ⑥Decarburization is carried out using the propylene carbonate method or PSA method, and it is advisable to conduct it in the third compression stage at an operating pressure of around 2.0 MPa ； ⑦Precision desulfurization uses the JTL-4 process ； ⑧Methanol synthesis is carried out using the low-pressure process at 5.0 MPa; there are various types of synthesis towers available for selection, and the synthesis off-gases are recovered ； ⑨A three-column process is suitable for methanol distillation. 2. The gas generation section: Since the required ratio for the raw gas used in methanol production is (H2–CO2)/(CO+CO2) = 2.05–2.15, and nitrogen in the raw gas is an inert gas, this section should produce water gas while minimizing the nitrogen content; therefore, the technological improvements in gas generation must aim to reduce the nitrogen content in water gas. The process flow and operation methods for gas production are basically the same as those in ammonia synthesis, but a separate water-gas holder is required to deliver semi-water gas and nitrogen-rich gas to two separate production systems. When modifying the gas generation system, special attention should be paid to the installation location of hydraulic valves and the specifications of all equipment, as well as to reducing the volume of the system in order to lower the nitrogen content in the water gas and decrease the amount of nitrogen-rich gas. The gas production process is still divided into six stages. The timing for transferring gas to the two gas tanks depends on the alcohol-to-ammonia ratio in production: when this ratio is high, less time should be allocated to transferring gas to the synthetic ammonia tank; whereas when the ratio is low, the time spent transferring gas to the methanol tank can be reduced, or even only the gas from the downstream stage needs to be sent to the methanol tank. It is desirable that the composition of water gas (CO + H2) be ≥90%, with (N2 + CH4 + Ar) ≤3.0%. When allocating the percentage of gas production, care should be taken to increase the downward blowing time in order to reduce the CH4 content in the gas. The gas generation capacity of the F2600 series gasifiers should reach 5,000 Nm3/h, which is equivalent to 10×10^4 t/year of CH3OH. With 8 such gasifiers in use, the coal consumption per ton of ethanol produced should be less than 1,350 kg. The gas generation system designed and upgraded by Shandong Linyi Chia Tai Thermal Energy Research Institute and Shandong Planning Institute for Shandong Jiutai Chemical features a unique structure, process configuration, and microcomputer program for its gas generators, achieving advanced technical and economic standards and yielding significant benefits. Blowing air recovery still requires an oxidizing gas, while the CH4 content in the off-gases from methanol synthesis and vent gases is low, resulting in a low calorific value of these gases, which differs from that in ammonia synthesis. One solution is to adopt a process that requires less combustion gas, by reusing some of the off-gases from the ammonia synthesis system ； Secondly, a blow-air fluidized mixed-combustion furnace is used to enable the waste residues and ash generated during gas production to be combusted together, thereby serving as a combustion aid. 3. Shift unit: Methanol production requires the CO content in the shift gas to be between 20% and 25%. The gas-to-gas ratio during the CO shift process is low, at around 0.15, and the requirements can be met with just one shift stage. 3.1 Selection of conversion process: Currently, for medium-shift catalysts, the required vapor-to-gas ratio is ≥0.35. If this ratio is too low, the Fischer-Tropsch reaction occurs in the Fe–Cr-based catalysts; as a result, ferric oxide in the catalyst is reduced to metallic iron, which destroys the catalyst’s crystal structure, reduces its strength, diminishes its activity, shortens its lifespan, and may even lead to a series of side reactions that produce carbonyl compounds, posing a threat to subsequent production processes. Moderate-temperature catalysts are not suitable for methanol production; a fully low-temperature shift process should be employed instead. In the full low-temperature conversion process, the low inlet temperature causes oil bubbles to remain undevaporated and settle between the catalysts, which is detrimental to maintaining catalyst activity and reducing resistance; therefore, it is important in this process to cool and remove oil from the gas before it enters the system. The low-temperature conversion catalyst belongs to the molybdenum-diamond series, and its activity requires an adequate supply of H2S; generally, the H2S concentration in the inlet gas should be at least 50–70 mg/m3, while that in the outlet gas should be around 150 mg/m3. Otherwise, a reverse sulfidation reaction will occur. In the full low-temperature methanol shift process, due to the low conversion rate, the conversion rate of organic sulfur also decreases. To reduce the content of organic sulfur in the shifted gas and thereby lessen the operating load on the desulfurization unit, it is advisable to install a medium-temperature COS hydrolyzer after the shift reactor, with an inlet temperature of 150°C to 200°C. The loading of the low-temperature shift catalyst and antidote is preferably done in two stages; cooling is carried out between these stages, and the heat of reaction is utilized promptly to prevent heat from accumulating later on. 3.2 Selection of conversion pressure The conversion pressures are 0.8 MPa and 2.0 MPa; the reaction is an equimolecular reaction, and pressure has no effect on the equilibrium of this conversion reaction. Both high and low operating pressures have their advantages and disadvantages. The main advantage of higher pressure is an improved conversion efficiency and a smaller equipment size; being at the same level as the decarburization pressure, it helps to reduce the operational power consumption resulting from increased compression due to the expansion of volume during the conversion reaction. The main disadvantage of increased pressure is the operational discomfort and intensified equipment corrosion resulting from it being different from the traditional pressure of 0.8 MPa. The advantages and disadvantages of increasing the methanol shift pressure (including shift dehydration) are not as pronounced as those in ammonia synthesis. Since the shift conversion rate in methanol production is less than 40%, the volume increase is small, and there is no need for a saturated hot water tower, which reduces equipment corrosion as well. In my opinion, for methanol production capacities of ≥10×10^4 tons per year, it is feasible to consider increasing the pressure to 2.0 MPa; for lower capacities, operating at the traditional pressure of 0.8 MPa ensures more stable production. 3.3 Selection of saturated hot water towers With the use of low-temperature, highly active catalysts and the full low-temperature shift process, the CO content in the shifted gas increases, while the steam consumption decreases. As a result, the amount of steam carried away by the shifted gas is reduced, weakening the function of saturated hot water towers for waste heat recovery; these towers have thus lost their relevance ； If it is retained, it will cause numerous side effects; therefore, a saturated hot water tower should not be kept in methanol production converters. 3.4 Regulation of CO content in the shift gas: Although the full low-temperature methanol conversion process is simple, regulating the CO content and temperature in the shift gas is more difficult than in ammonia synthesis systems; especially when the load changes, large fluctuations often occur. Therefore, the all-low conversion process should take into account the necessary secondary adjustments for temperature and converter gas composition. 3.5 Adjustment of shift gas desulfurization: If shift gas desulfurization increases with shift pressure, a higher pressure for wet desulfurization is favorable for H2S absorption, but it is not conducive to the regeneration of the rich liquid. For the export rich liquid, it is necessary to ensure proper release of the flashed CO2 gas; the structure of the spray regeneration equipment as well as the operating parameters must be adjusted to enhance the regeneration effect. 4. In the decarbonization section, a certain level of CO2 content should be maintained in the gas phase of the methanol synthesis reaction. The presence of CO2 enhances the activity of the catalyst; moreover, its participation in the reaction helps to control and stabilize the bed temperature, while also suppressing side reactions. The CO2 content is preferably between 1.0% and 3.0%, so the requirements are not as stringent as those in ammonia synthesis, allowing for a relatively greater flexibility in the choice of decarburization methods. There are currently many decarbonization methods used in nitrogen fertilizer production. Among these methods, at a pressure level of 2.0 MPa, where the CO2 content in the purified gas is kept at a certain level and low energy consumption is a key consideration, the physical absorption PC method is the preferred choice. The PC process is mature; it requires no heat or cold during production. Methanol production demands a low level of purity, and its power consumption is significantly lower than that of ammonia synthesis. Additionally, due to its low investment cost and stable operation, the PC process is an appropriate choice for wet carbon removal. With the advancement of industry technology, the PSA method has also developed rapidly. The main advantages of the PSA method are power savings, simple operation, and no environmental pollution. The obstacles to the widespread use of the PSA method are high investment costs and significant losses of CO gas. However, for methanol production, decarbonization requires only one stage of pressure swing adsorption, and the CO2 does not need to be purified for use; this greatly simplifies the equipment, resulting in investment costs that are slightly lower than those of the PC process. As for CO gas loss, recent advancements in PSA technology in terms of process control and the modification of program valves have led to a significant reduction in CO loss rates. By comparing the loss of major active gases in the PC method and the PSA method, at a flashing pressure of 0.4 MPa, the amount of flash gas produced by the PC method is 200 Nm3/tCH3OH. In the PSA process, the main source of effective gas loss is the desorption of air, with a gas volume of approximately 550 Nm3/tCH3OH. Thanks to technological advancements, the concentration of (CO+H2) can be kept below 8%, resulting in an effective gas loss of 44 Nm3/tCH3OH. Of course, leaks from programmable valves are also a factor contributing to gas loss; these leaks can be minimized through appropriate measures. Other sources of loss, such as those related to the recovery of gas from pipelines and at the bottom of towers, are also given due attention. In both of these decarburization methods, the flash vapor and the desorbed exhaust gas can be used to recover H2, which contributes to reducing production costs. Currently, manufacturers have the option of either of the two decarbonization methods, and both achieve good technical and economic performance. 5. The purification section: The alcohol-ammonia process is similar to the hydroxylamine process, and the feed gas requires thorough purification. Gas purification primarily involves the removal of sulfur, with the requirement that the total sulfur content in the feed gas entering the tower be ≤0.1×10‑6. Regarding gas purification, the Hubei Provincial Institute of Chemistry has made significant contributions; the JTL-4 process technology should be adopted. It is important to note the following: ① Make good use of the EH-2 medium-temperature sulfur-resistant hydrolysis catalyst with low temperature sensitivity to remove organic sulfur, control the temperature of the gas entering the tower, and take full advantage of its high activity at medium temperatures in order to reduce the load on subsequent desulfurization processes. ②Chlorine and chlorides, metal carbonyls, and oil contaminants can also cause catalyst poisoning and even pose fatal risks. The deep purification of gases involves dechlorination and the removal of metal carbonyls; an appropriate amount of EF-3 and EF-7 catalysts should be used in the purification fillers. 6. Methanol synthesis section: The selection of the methanol synthesis tower and the design of its process flow are important. The prosperity of the methanol market in recent years has prompted China’s research institutions to develop various types of methanol synthesis towers suitable for the production of ammonia and hydrazine from medium and small-scale nitrogen fertilizers. The selection of methanol synthesis towers should take into account domestic conditions, as this helps to reduce investment costs, accelerate project implementation, and achieve quick results, in line with the basic guiding principles of technological transformation. Significant progress has been made in methanol synthesis technology that possesses independent intellectual property rights in our country. With the development of low-pressure and low-temperature copper-based catalysts, low-pressure methanol synthesis technology, thanks to its low energy consumption and reduced investment requirements, has gained an advantage; as a result, the development and adoption of medium-pressure synthesis methods have become even more advantageous. The synthesis of methanol from CO and H2 is a highly exothermic reaction with reversible volume reduction. Based on the method used to remove the heat generated by the reaction, there are two types of synthesis towers: gas-cooled and water-cooled ones. Each of these methods has its own advantages; for example, the Jw low-pressure homogenization type features a small volume, high CO conversion rate, and uniform temperature across the catalyst bed, making it suitable for large-scale methanol production. In a water-cooled methanol tower, the reaction bed is located in boiling water, with reaction tubes separating the two. The reaction products are carried away by the boiling water and converted into water vapor. This type of tower does not require an electric furnace; the synthesis reaction and heat recovery are integrated, simplifying the process flow. It is easy and stable to adjust the temperature of the catalyst bed as well as the steam pressure, making it most suitable for applications with an annual production capacity of 100,000 to 200,000 tons. Water-cooled types are further divided into shell-and-tube and tube-type types, with the difference lying in whether the reaction bed is inside or outside the tubes. The reaction bed layer of the Lurgi tower used in the earlier stage is of the shell-and-tube type inside the tubes. Compared to the JDJ tubular bed developed by Hunan Anchun High-Tech Co., Ltd., it has greater advantages outside the tubes. ①The catalyst bed is placed outside the tubes, resulting in a high volume utilization factor; this means that the diameter of the tower can be kept relatively small, which helps to reduce costs associated with investment, transportation, and installation. ②The bed layer is located outside the tubes, resulting in a radial flow pattern throughout the tower. This configuration reduces tower resistance and temperature rise, which helps to lower operating power consumption and improve the purity of the alcohol. It also offers great operational flexibility and high production capacity. ③The tube bundle is of the suspended type, meaning one end is fixed while the other can stretch freely; ordinary stainless steel tubes are used for the tubes, and composite steel plates are used for the shell, whereas shell-and-tube designs require higher-grade materials. ④Additionally, it has certain advantages in terms of advanced and mature technology, easy operation and adjustment, and low operational energy consumption. Importantly, the intellectual property rights are clear, and there is a one-stop service covering design, production, and on-site technical support, which facilitates low investment, rapid implementation, and early results. Multiple JJDФ2800 methanol towers have been put into operation; Shandong Deqilong Group’s first two units were brought online earlier, and they are performing very well. These units feature low system pressure, low resistance, low power consumption during operation, and stable performance, all of which indicate significant energy-saving benefits. The steam generated as a by-product of tonal alcohol amounts to over 1.2 tons, bringing significant benefits to the company. After investigation and research, Mingshui Dahuahua Group decided to use the JJD tubular methanol tower. 7. Methanol distillation section: The methanol distillation process should employ a three-column system, with the main equipment being a pre-distillation column, a pressurized column, and an atmospheric column. The three-tower process can reduce impurities in pure alcohol, improve the quality of methanol, and enhance heat utilization efficiency. For tower structures, regular packing and tray plates (vertical plates) are preferable, which can reduce steam consumption by 1.1 to 1.2 tons per ton of alcohol. The residue generated by distillation contains a small amount of methanol and its fusel oils, and has a high COD value; it represents a major environmental pollution source in methanol production. Plants that produce 100,000 tons of methanol per year generate more than 50,000 tons of such residual waste. As the source of pollution, it is the duty of such entities to carry out remediation efforts, and in this regard, the Xuzhou Water Treatment Research Institute has achieved remarkable results in the treatment and recycling of residual liquids. The residual liquid is pre-treated, the pH value is adjusted, it undergoes precise filtration, softening and hardness removal, and oxygen scavengers as well as corrosion inhibitors are added; these can be recycled within the production system. The treatment of pollution from residual liquids is an important aspect of environmental protection, and it is also a requirement for the survival and development of enterprises; therefore, it must be given due attention. The management of residual waste is a systematic task; to completely eliminate the risks posed by pollution, continuous efforts and a lot of work are still required. 8. Regulation of the production system: In ammonia synthesis production systems, most enterprises adopt the hydroxylamine process. With the adoption of this hydroxylamine-based process, both series and parallel processes for alcohol production are available; therefore, a unified production scheduling and control system should be established for both methanol and ammonia synthesis production. The ammonia synthesis and polyol production process should make full use of its advantages; the alcohol-to-ammonia ratio should be adjusted to an appropriate economic range depending on the specific production conditions, so as to achieve high yields of polyols while reducing the energy consumption in ammonia synthesis. Production experience has shown that this process represents a technically sound improvement project with significant benefits. The production of alcohols and hydrazines should be integrated organically with the ammonia synthesis system, thereby leveraging the advantages of methanol production in nitrogen fertilizer plants. The nitrogen-enriched gas generated from alcohol hydrazine must be recovered in order to reduce its amount, thereby lowering the consumption of coal as a raw material for ammonia synthesis and minimizing the nitrogen content in methanol gas. A large amount of nitrogen-rich gas is recovered and fed into the ammonia synthesis system, which affects the gas production capacity of the ammonia synthesis furnace as well as the regulation of the hydrogen/nitrogen ratio; therefore, it is essential to modify the methanol gas production process in order to reduce the amount of nitrogen-rich gas. Methanol synthesis system, where (N2+CH4+Ar) are inert gases; its vent volume VVent (m3/h) is related to the amount of inert gases in the fresh gas and recycled gas. Generally, the alcohol off-gas volume per ton exceeds 500 m3, and this is an important factor affecting methanol production and consumption. Such a large amount of vent gas being recycled to the ammonia synthesis system affects the stability of ammonia synthesis production as well as the balance of the compression system; therefore, the amount of vent gas should be minimized. The measures include reducing the nitrogen content in the methanol production gas, increasing the inert gas content in the synthesis cycle gas, adjusting the levels of CO and CO2 fed into the methanol synthesis system in a timely manner, and minimizing fluctuations in temperature and pressure. In production, although alcohol hydrazine and synthetic ammonia operate as two separate systems, there is still the issue of a proper alcohol/ammonia ratio in terms of overall production, though this ratio is larger than that in the case of alcohol alone. When the alcohol ratio is too high, ammonia synthesis cannot withstand the recovery pressures associated with nitrogen-rich gas and off-gases, making it more difficult to improve overall production efficiency. The exhaust gas from alcohol synthesis should have H2 removed and recovered, while the remaining gas is sent to the blower for combustion support. The indicators of CO% in the transformed gas, CO2% in the decarburized gas, and the inert gas content in the alcohol synthesis cycle gas should be adjusted promptly. Generally speaking, at the beginning of production the catalyst is highly active, resulting in a lower CO% level and a higher CO2% level. When the catalyst activity is low, a higher CO2% will remain and accumulate, resulting in an increased vent volume. The content of inert gas in alcohol synthesis is similar to that in ammonia synthesis; the catalyst has good activity, allowing for an appropriate increase. The theoretical requirement for syngas production from monohydric alcohols is: (H2－CO2)／(CO2＋CO)＝2.05－2.15. In actual production, adjustments should also be made as appropriate based on catalyst activity and temperature control, with further improvements expected in the later stages of production. Alcohol hydrazine should make use of shared facilities in production as much as possible to reduce investment. The purification of alcohols should be determined based on the capabilities of the distillation process and the required quality of the pure alcohol. Due to the differences in the catalysts used and the operating pressures in the production of hydrazine and dihydrazine, the levels of by-products vary; they are higher in the case of hydrazine production. There are also differences in the process conditions during the distillation of crude alcohols, which makes it inappropriate to use the same distillation methods for both. The use of coal as a raw material in the hydroxylamine process for producing methanol-based nitrogen fertilizers offers certain advantages; however, hydroxylamine production is still in its early stages, and a period of adaptation and further understanding is required. The design of this process as well as its management need to be improved, and it is necessary for professionals to enhance communication and research in order to elevate hydroxylamine production technology to a new level.