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1 Overview of the Dimethyl Ether Plant of Ningxia Coal Group: The 210 kt/a dimethyl ether plant of Shenhua Ningxia Coal Group is part of the 830 kt/a dimethyl ether plant and serves as one of its components. The preliminary construction and testing of this facility were carried out in advance, mainly to support Project No. 1 being developed by the group at the Ningdong Heavy Chemical Industry Base – a 250 kt/a methanol project that uses coal as raw material. Its purpose is to alleviate the pressure exerted by methanol production facilities and their operating costs during periods of weakness in the methanol market, while also adjusting the product portfolio to enhance market competitiveness. The facility is located near the finished product tank area of the methanol plant, and its design concept is to use the methanol produced by the 250 kt/a methanol project to manufacture dimethyl ether through a dehydration reaction. The plant utilizes the fixed-bed catalysis technology developed by TOYO ENGINEERING CORPORATION in Japan. The entire plant is divided into four sections: the methanol vaporization system, the dimethyl ether reaction system, the distillation system, and the dimethyl ether product storage tank system. Construction of the facility began in March 2006, with Huasa Sanjian and Shisan Jian taking charge of the work; at the same time, orders were placed for large-scale, long-cycle equipment. Completion of the project was achieved in October 2007, followed by a successful first operation on December 24, during which qualified dimethyl ether product was produced, whose quality met all the requirements of the CJ/T259-2007 standard. This is the largest coal-to-dimethyl ether production facility currently in operation across the country and even the world. The successful commissioning of this project has also filled the gap in Ningxia, where there was no production of dimethyl ether, a new type of fuel and chemical raw material. 2 Issues to Consider in Project Construction: Since this project utilizes ready-made methanol as raw material for further processing, the number of pieces of equipment is low – there are only 57 units in total. Additionally, as the design pressure of the equipment is not high (the maximum pressure is 1.1 MPa), the construction process is not particularly challenging. In the specific project construction, the following issues should be given primary attention. (1) Manufacturing and installation of dimethyl ether spheres: Due to their large size, dimethyl ether spheres cannot be manufactured at the manufacturer’s site and then transported to the installation location. At the same time, this equipment is a Class III pressure spherical vessel; therefore, its shell can only be manufactured by the manufacturer and transported to the site before assembly. Due to the constraints of the construction site conditions, this task is a key item in the project construction and requires strict oversight. (2) Strict control of construction quality: Due to the hazardous properties of dimethyl ether, all moving equipment in the design is specified as shielded pumps or magnetic drive pumps to ensure no leaks. These pump units have high requirements regarding the cleanliness of the medium; therefore, during installation, proper attention must be paid to any debris in the pipelines. In particular, the pipes located behind the inlet filters and in front of the outlet valves of the pump units must be removed and thoroughly cleaned. Additionally, a thorough inspection of the interior of the pump units is necessary. 3 Precautions for initial operation: Due to issues such as the arrival of heaters at the start of construction, this project was not fully completed until October 2007, after which it entered the stage of \"three inspections and four fixations\" for the installation. Work such as plant purging, water flushing, loading of the dimethyl ether reactor catalyst, system airtightness testing and replacement, system verification and instrument calibration, DCS system calibration, and system water testing will only begin in November. By late December, the unit entered the commissioning phase; methanol was fed into the system, and the dimethyl ether catalyst was used to raise the temperature with nitrogen. After nearly 4 days of testing, the system operated normally, and its load was increased to the design specifications, enabling the production of dimethyl ether product. The product composition is 0.86% methanol, 0.092% water, with a purity of 99.02%. It fully meets the requirements specified in CJ/T259-2007 \"Standard for Dimethyl Ether Used in Urban Gas\" (Industry Standard for Urban Construction of the People’s Republic of China), namely a dimethyl ether content of 99.0% or higher, a methanol content of less than 1.0%, and a moisture content of 0.5% or less. The commissioning of this facility marks the production of another new chemical product in Ningxia. It is also the largest dimethyl ether production plant in the world at present, as well as the first dimethyl ether production plant using coal as raw material developed by Toyo Company, which possesses proprietary technology for dimethyl ether production. The successful trial operation of this facility also marks the success of Shenning Group’s second chemical project. This lays the foundation for enhancing the competitiveness of the group’s chemical products, improving their product structure, and achieving better economic benefits. Looking back at this test run, since most of the pipelines in the dimethyl ether plant are filled with methanol or dimethyl ether, many of these pipelines did not have heating and insulation systems installed. This made the test run in winter particularly difficult; especially the processes of purging the plant, ensuring airtightness, and performing water flushing were extremely challenging, and the safety pressures involved were very high. It was precisely because of these difficulties that we gained a great deal of experience, which is outlined below. 3.1 System purging stage: (1) Before purging the equipment, try not to remove the purging ports; wait until the system reaches a certain pressure and all drainage valves in the equipment and pipelines are opened, so as to drain as much water as possible from the system (mainly the water remaining from pipeline pressure testing), thereby preventing blockages in the pipelines during the purging process. (2) Blowing should preferably be carried out using explosive blowing, so that water accumulated within the system can be carried away by the airflow or to the vicinity of the blowing port. (3) It is recommended to purge the steam pipeline in advance before purging the device; once the purge is successful, the steam pipeline should be put into use promptly so that temporary hoses can be connected to the purge ports to thaw the ice, thereby ensuring the quality and progress of the purge process and enabling it to proceed smoothly. (4) Knocking out the pipeline is crucial during purging, as some water carries solid particles, slag, and other substances that get frozen on the pipe walls. (5) Make full use of the relatively ample afternoon light to carry out purging. The purging medium should preferably be dry plant air or nitrogen. 3.2 System water commissioning (1) Before water commissioning, the system must undergo a strict airtightness test; it can proceed only after passing this test. (2) Use condensate or water heated by steam for flushing and operation to prevent freezing during operation. (3) In water intermodal transport, some instruments such as pressure gauges and level gauges at the inlet and outlet of pumps must be protected against freezing by wrapping them with temporary steam hoses or by allowing a slight amount of fluid to flow out, in order to prevent false readings from these instruments. (4) For rotating equipment (pumps that cannot be checked by manual rotation), it is advisable to connect steam or hot water hoses before starting up, in order to preheat the pump body and ensure it is fully ready before operation. This prevents accidents such as freezing inside the pump and resulting damage to the equipment. (5) In the water commissioning process, it is possible to decide whether to carry out chemical cleaning based on the actual conditions of the equipment. If cleaning is necessary, it can be done after the initial water commissioning, but it is essential to conduct scale testing first, as well as take measures to protect the instruments and internal components. (6) Cleaning this system is very important; therefore, the water circulation should continue for as long as possible to maintain the system’s cleanliness. Meanwhile, during the water circulation process, the frequency of cleaning the filters at the inlet of the pumps should be increased to ensure the safe operation of the mechanical equipment. (7) Efforts should be intensified to remove ice from the site and clear standing water, in order to prevent the equipment from freezing; otherwise, it will pose additional risks to the safety of employees. (8) Systems and equipment that can supply heat to the system should be put into use as much as possible; in particular, the heat tracing system must be ensured to be operating properly. (9) After water interconnection, the system should be dried and purged promptly to prevent it from being contaminated or corroded again. (10) The airtightness test must be carried out rigorously to ensure the tightness of the system. 3.3 Catalyst heating and adsorption (1) Before heating the catalyst, as it is the first trial run, the methanol distillation system should be put into operation in advance to ensure its stable operation. (2) During the initial heating, in order to better understand the catalyst’s reduction behavior during heating and to become familiar with the operation procedures, the heating rate should be slower than what is recommended by the manufacturer. This allows for a proper understanding of the relationship between the opening degrees of various valves, thereby preventing uncontrolled heating of the catalyst due to excessive operational adjustments. (3) To make the first temperature increase more stable, the heating rate can be appropriately kept lower. The speed can be slightly faster before the catalyst temperature reaches 60°C; between 60°C and 100°C, the speed should be reduced appropriately to prevent damage to the catalyst caused by the rapid expansion of water adsorbed within it ； At the same time, during the heating process, sufficient gas volume and air velocity must be ensured to allow the catalyst bed to be heated evenly. At 100°C and 160°C, isothermal operation should be carried out to minimize the temperature gradient in the catalyst bed. (4) Before carrying out the adsorption operation, it is necessary to ensure that the temperature at the lowest point of the catalyst bed is above 130°C, in order to prevent localized water accumulation in the catalyst due to factors such as pressure fluctuations. (5) Steam should be added slowly. Each time it is increased, the temperature must be maintained stably. The adsorption process is considered complete only after the steam addition reaches the specified level, the system operates stably for at least 2 hours without any fluctuations in bed temperature. (6) During the catalyst heating process, attention should be paid to pipeline drainage. 3.4 Equipment Commissioning (1) Before commissioning, it is essential to ensure that the instrumentation system is functioning properly, as this is key to a safe commissioning process. (2) Make preparations for keeping all test run records. (3) Make thorough preparations for emergency response in case of catalyst overheating, system leakage, or fire. (4) The high alarm value for the catalyst bed temperature should be reduced in advance to alert operators to take action promptly. At the same time, to ensure continuous testing, the interlock for high bed temperature should be short-circuited. (5) Re-check the airtightness of the system to ensure it is satisfactory. (6) Ensure that the combustible gas detection system of the device is in proper and reliable operation; meanwhile, conduct manual analyses at regular intervals or as needed during the commissioning phase to ensure that the levels of various toxic substances in the environment remain within the allowed limits. The main toxic substances in this device are methanol and dimethyl ether; the concentration of methanol in the air is kept below 50 mg/m3, while that of dimethyl ether is kept below 400 mg/m3 ； Otherwise, the cause should be identified and eliminated promptly. (7) During the initial trial operation, the feeding temperature of the catalyst should be kept below 220°C, and the rate of temperature increase must be strictly controlled, especially at the onset of the reaction, to prevent a sudden rise in bed temperature that could not be controlled in time. Meanwhile, the nitrogen system and the steam system should be in good standby condition, ready to be activated at any time, to serve as emergency measures for dealing with rising bed temperatures. (8) After methanol is fed in, and before dimethyl ether is produced, the bottom temperature of the dimethyl ether distillation tower should be increased in advance to prevent light components such as dimethyl ether from entering the system and causing overpressure. It can also help the dimethyl ether distillation tower reach normal operating conditions sooner. (9) When there is a liquid level in the dimethyl ether reflux tank, full reflux should be initiated as early as possible to reduce the time required to obtain qualified products. (10) A buffer zone for defective products should be established in advance to prevent excessive accumulation of fluid in the system. (11) When the catalyst bed temperature rises sharply, pressure should be released immediately and steam or nitrogen should be introduced. Pressure relief has two advantages: on one hand, it increases the air velocity; on the other hand, as the temperature rises, side reactions of methanol increase, leading to an increase in gases such as carbon monoxide and hydrogen. Pressure relief helps prevent the system from becoming overpressured. In summary, throughout the commissioning of the dimethyl ether plant, system overpressure and catalyst overheating are the most common issues and also the hardest to control; strict prevention measures must be taken.