Gasification to produce gas: dust removal and purification

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A two-stage washing tower is used for washing and cooling, followed by venturi dust removal; separation in a separator ensures that the standards are basically met

Let’s use filtration for it; the specific operating conditions aren’t very clear to me. I think filtration is the way to go, and we can discuss this together

For dust removal in the gas produced by brown coal gasification, the gas contains tar and is prone to coking. The purification of blast furnace gas typically involves ammonia water spraying for washing, cooling, and dust removal. Compared with blast furnace gas purification, your process involves higher pressures; it is recommended to use cyclone dust removal, with steam heating applied outside the cyclone along with proper insulation to prevent the precipitation of tar and coking. We have handled dust removal in similar working conditions; feel free to contact me if needed – my name is also my QQ number.

A granular layer dust collector is used, with quartz sand as the filter media

This post was last edited by luoli519 on 2016-2-25 at 11:30. Washing towers, high-temperature filter elements, and electrostatic precipitators (for removing dust and tar) are the final stages in the purification process of high-temperature coke oven gas and raw gas. 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 off thousands of attackers\"; after all, the washing tower, ceramic filters, and electrostatic precipitators all serve the purpose of carrying out detailed cleaning tasks – they represent 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: use dry methods whenever possible, and avoid introducing a three-phase solution when a two-phase solution will suffice. 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 cyclonic 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, to remove 99.99% of dust particles with a size 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, namely a primary pre-filter equipped with a backup unit, combined with a secondary precision coalescing filter that also has 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 droplet 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 the internal components on a regular basis, which requires additional capital investment. 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 operational and maintenance costs for the system. The second approach involves using electric capture equipment directly, namely a primary electric captor equipped with a backup unit, along with a secondary electric captor also equipped with a backup unit. The gas that passes through the secondary electric captor 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 electrostatic precipitators require consideration for high-temperature insulation, high-temperature sealing, high-temperature corona effects, as well as the tendency of electrodes to become covered with particulates, and since they can function stably only in typical aerosol environments, their application is relatively limited. Regular replacement of internal components is necessary, which entails additional capital investment; moreover, the operational and maintenance costs 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 by the upstream dust removal equipment, a first-stage fixed venturi washer plus 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, agglomering them, and causing them to grow larger. The washing water, liquid droplets, as well as the wetted and agglomerated dust particles are then removed from the gas phase using the first-stage multi-factor cyclone separator ； In the approximately 8%~10% of the airflow that escapes, a small amount of residual particles are still present. These particles pass through a secondary adjustable venturi washer along with 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 and agglomerating them so that they grow larger. The washing water, liquid droplets, and the wetted and 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 even the smallest amounts of dust. At the gas outlet at the top of the scrubber, an efficient vane-type demister must be installed to remove any liquid droplets or sludge present in the airflow, ensuring that the amount of solids carried in the airflow 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 mother-son 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 method: 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 swirl parent-child separator + 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. 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 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. We welcome colleagues to engage in in-depth discussions, and please visit our official website to learn more about our proprietary specialized separation technologies and equipment.