Gasification dust removal issues

Cyclone separator............................

A fluidized bed can use a cyclone. It is generally washed with water, and ceramic filtration is also used

Could you share the advantages and disadvantages of each?

For the quenching process: cyclone separator, venturi, followed by a washing tower; for the non-quenching process: ceramic filter. BGL: An electric tar capture separator is used.

This post was last edited by luoli519 on 2016-2-25 11:28. It’s a very meaningful topic. I have seen that for some owner-funded projects, the providers and designers of the process technology packages for various units such as the gasification unit, conversion unit, purification unit, and synthesis unit are different; therefore, it is very important to choose a competent overall design agency. I feel that some of the overall design institutes (and even the project owners) lack the comprehensive coordination capabilities needed to manage the entire project as well as the technical design teams involved in various components. For example, their overall strength and capabilities, along with their experience in project design and operation, are not on par with those of the technical design institutes handling individual components. Considering the responsibilities associated with the risks in the operation of its own unit design, the Unit Technology Design Institute often sets relatively strict requirements for the input conditions of its own unit (that is, the output results of the previous unit). I have also reviewed the technical specification documents for the gasification units and conversion units of certain projects, and I noticed that the requirements imposed by the conversion unit on the gas fed into this unit – that is, the gas coming out of the gasification unit after purification – are that the dust content in the dry gas must be less than 3 mg/Nm^3, and the amount of liquid droplets carried in the gas must not exceed 1 mg/Nm^3. The reason is to prevent dust carried in the purified gas produced by the gasification unit from accumulating at the inlet section of the pre-conversion reactor, thereby hindering the proper operation of that unit. Looking back on those years with the projects for producing synthetic ammonia and methanol from coal (300,000 tons per year, 500,000 tons per year, 800,000 tons per year, 1.2 million tons per year), it seems that no such strict requirements were ever set. Moreover, in terms of both cost and operating expenses, the conversion unit cannot be compared to the gasification unit; why then force the gasification unit to meet such strict requirements, which ultimately leads to increased operating costs for the entire project? Moreover, isn’t there in the gas inlet section of the pre-conversion reactor a series of ceramic balls of different sizes and heights to serve as inert sections? Isn’t the catalytic reaction section also equipped with various combinations of active sections? Couldn’t the pre-conversion reactor and the main conversion reactor be designed using a hybrid process? From the perspective of the overall economic efficiency of the owner’s future projects, I believe that it is possible to mitigate the stringent requirements on gas supply from the upstream gasification units through competitive optimization and innovative design of unit process combinations. Even if that’s not the case, I’m not the owner; I’m either the supplier of the unit process package or the design institute. Therefore, the suppliers of the gasification unit process package and the design institute must earnestly comply with strict gas supply requirements. Therefore, whether it is a quenching process, a non-quenching process, or liquid slag discharge, it is necessary to meet the requirement of \"extremely low levels of dry-based gas dust and liquid droplets\". The scrubber tower, high-temperature filter elements, and electrostatic precipitators (for dust and tar removal) serve as the final stages in various slag-gasification processes. But obviously, it is not feasible to rely solely on each of these final treatment stages to achieve a situation where \"one person can hold back thousands of attackers\"; after all, the scrubber towers, ceramic filters, and electrostatic precipitators serve the purpose of carrying out detailed cleaning tasks – they are economic solutions for achieving precise dust removal from air streams containing trace amounts of dust. If these devices were expected to handle both rough and delicate cleaning tasks, it would make the operation of such systems too expensive. So how is that “rough work” done? The principle is to avoid wet methods whenever possible, and to opt for two-phase solutions rather than introducing three-phase solutions. This is because high-temperature wet dust removal not only requires a large amount of desalinated water, but also needs it for heat recovery, and the post-treatment process is complicated. For dry processing to carry out the ‘rough work’ of removing the vast majority of dust and liquid droplets, barrier-type equipment cannot be used (as its flow surfaces tend to get clogged), and instead dynamic cyclone methods must be employed to separate large amounts of dust and liquid droplets from the hot gas stream. Among the equipment for cyclone-based gas-solid (liquid) separation technologies, the multi-factor cyclone parent-child separator offers significant advantages over traditional cyclone separators in terms of separation accuracy, depth, operational flexibility, and equipment size. Based on my many years of experience and data from domestic and international design platforms for cyclone-based gas-solid (liquid) separation, it is feasible to achieve 4N-level separation of solid particles with a size of 5 microns – that is, 99.99% removal of dust particles of 5 microns or larger. Particles with a size of 3 microns or less exhibit significant Brownian behavior; the smaller the particle diameter, the more pronounced this behavior becomes, making separation through dynamic methods increasingly difficult. Particles of 3 microns and smaller, especially those tiny dust particles whose apparent density is already very low, preventing them from coalescing and growing larger due to surface tension. What are the effective methods for separating it from the gas phase? The first approach is to use high-temperature filter elements directly, that is, a primary pre-filter equipped with a backup unit combined with a secondary precision coalescing filter also equipped with a backup unit. The gas passing through the secondary precision coalescing filter must meet the requirement that the solid load be below 3 mg/Nm^3, and the liquid mist load must not exceed 1 mg/Nm^3 (as per process requirements). Since the filter elements are prone to clogging with dust, it is necessary to consider replacing them regularly, which requires additional investment in equipment. There are also ongoing costs associated with the procurement of spare parts for maintenance. In particular, coalescing filter elements are much more expensive than regular filter elements, resulting in high costs for the operation and maintenance of such systems. The second approach involves using electric capture equipment directly, namely a first-stage electric captor equipped with a backup unit, followed by a second-stage electric captor also equipped with a backup unit. The gas exiting the second-stage electric captor must meet the requirement that the solid load be below 3 mg/Nm^3, and the liquid droplet load must not exceed 1 mg/Nm^3 (as per process requirements). Since electrostatic precipitators require consideration for high-temperature insulation, high-temperature sealing, high-temperature corona effects, as well as the issue of electrodes being easily covered by particulate matter, and since they can only function effectively in typical aerosol environments, their application is relatively limited. Regular replacement of internal components is necessary, which leads to increased capital costs for equipment, and the operational and maintenance expenses for such systems are also high. The third method is to use demineralized water in a wet process to remove dust. In some process packages, as soon as the gas stream exits the gasifier, it is washed in a spray scrubber using deionized water to remove large-sized dust particles. I don’t agree. Wet high-temperature dust removal requires a large amount of desalinated water, and it is not economical to use such expensive desalinated water in situations where it isn’t necessary (where dry cyclone dust separators can be used). After the initial dust removal process carried out by the upstream dust removal equipment, a first-stage fixed venturi washer and a first-stage multi-factor cyclone separator are used. In the first-stage venturi washer, large amounts of high-speed deionized water are used to break up the tiny dust particles, thereby wetting them, agglomerating them, and causing them to grow larger. Subsequently, the washing water, liquid droplets, and the dust particles that have been wetted, agglomerated, and enlarged are removed from the gas phase using the first-stage multi-factor cyclone separator ； There is still a small amount of material remaining in the airflow that has escaped, accounting for roughly 8% to 10%. This remaining material passes through a secondary adjustable venturi washer and a secondary multi-factor cyclone separator. In the secondary adjustable venturi washer, high-speed desalination is used to break up the tiny dust particles, thereby wetting, agglomering, and enlarging them. The washing water, liquid droplets, as well as the wetted, agglomerated dust particles are then removed from the gas phase using the secondary multi-factor cyclone separator. After treatment with a two-stage adjustable venturi scrubber + a two-stage multi-factor cyclone separator, approximately 0.05% of even finer dust particles remain in the airflow; therefore, the following method is required: 1. Electrostatic dust collection (no additional equipment needed) ； Or 2, Precision coalescing filter (no spare unit required) ； Or 3: An immersion-type scrubber is used to capture extremely small amounts of dust; in addition, an efficient vane-type demister must be installed at the gas outlet at the top of the scrubber to capture any liquid droplets or sludge present in the gas stream. This ensures that the amount of solids carried in the gas stream is below 3 mg/Nm^3, and that the amount of liquid droplets does not exceed 1 mg/Nm^3 (as required by the process specifications). Therefore, following the above approach, the process should proceed as follows: Step 1 – Dry method: A1: Gasification furnace + multi-factor cyclone parent/child separator + primary filter (with spare unit) + secondary coalescing filter (with spare unit). Advantages: 1. Reliable product quality ； 2. Less desalinated water is used. Disadvantages: High investment and high operating and maintenance costs. A2: Gasifier + multi-factor swirl separator for mother liquor separation + primary electrostatic precipitator (including spare unit) + secondary electrostatic precipitator (including spare unit). Advantages: 1. Less desalinated water is used. Disadvantages: High investment and high operating and maintenance costs. II. Wet process: B1: Gasification furnace + jet scrubber + primary fixed Venturi scrubber and primary multi-factor swirl parent-child separator + secondary adjustable Venturi scrubber and secondary multi-factor swirl parent-child separator + scrubber tower. Advantages: 1. Reliable product quality ； 2. Low investment, no spare parts required. Disadvantages: 1. A large amount of desalinated water is required. III. Wet-dry hybrid method: C1: Gasification furnace + primary multi-factor cyclone mother-son separator + primary fixed venturi scrubber and primary multi-factor cyclone mother-son separator + secondary adjustable venturi scrubber and secondary multi-factor cyclone mother-son separator + scrubber tower. Advantages: 1. Reliable product quality ； 2. Low investment, no spare parts required. Disadvantages: 1. A large amount of desalinated water is required. C2: Gasifier + primary multi-factor swirl mother-son separator + primary fixed venturi scrubber and primary multi-factor swirl mother-son separator + secondary adjustable venturi scrubber and secondary multi-factor swirl mother-son separator + electrostatic precipitator (no standby unit required). Advantages: 1. Reliable product quality ； 2. The investment and operation and maintenance costs are moderate. Disadvantages: 1. A certain amount of desalinated water is required. C3: Gasifier + primary multi-factor swirl mother-son separator + primary fixed venturi scrubber and primary multi-factor swirl mother-son separator + secondary adjustable venturi scrubber and secondary multi-factor swirl mother-son separator + secondary precision coalescing filter (no backup unit required). Advantages: 1. Reliable product quality ； 2. The investment and operation and maintenance costs are moderate. Disadvantages: 1. A certain amount of desalinated water is required. We welcome colleagues to engage in in-depth discussions, and please visit our company’s website to learn more about our advanced separation technologies and equipment.

Well-organized and enlightening. Thank you!