Process comparison between coal tar fluidized-bed hydrogenation and fixed-bed hydrogenation

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This post was last edited by liuquan1100 on 2017-12-29 at 14:21. The raw material is the full distillate of medium- and low-temperature coal tar; the plant’s processing capacity is 100,000 tons per year. The operating pressure of the hydrogenation system is 16.6 MPa (G), in order to meet the product quality requirements specified by China’s National V standards for gasoline and diesel products as mandated nationwide in 2016. Based on its previous experience in processing coal tar, Shanghai Xinyou Energy Technology Co., Ltd. knows that coal tar has a high density, a high C/H ratio, as well as high levels of sulfur, nitrogen, and resinous asphaltenes; these properties make it easy for the material to cause coking, thereby blocking equipment and pipelines, and thus making its processing difficult. To this end, two processing options are provided for comparison. (1) Option 1: Fixed-bed hydrogenation process. Key points of this option: Coal tar is separated from coal tar pitch, and then the mixture undergoes two stages of hydrogenation – refining and hydrocracking – to produce high-grade refined oil products. A hydrogen production plant with a capacity of 10,000 Nm3/h is provided. For coal tar hydrogenation units, the most mature process currently in use is the one that involves \"atmospheric and vacuum pretreatment + hydrogenation refining + hydrocracking of residual oil\". First, the asphalt, solid impurities, and moisture that are not suitable for processing in fixed-bed hydrogenation are removed, after which the residual oil at 350°C is sent to the hydrocracking system. The fraction with a temperature >350°C, after hydrogenation refining, enters the hydrocracking system, where large molecules are opened and cracked into smaller molecules (naphtha, diesel fractions). The products of this cracking reaction are sent to a product distillation column for separation. In this process, the selectivity of the catalyst must not only enable the ring-opening and cracking of polycyclic and fused-ring hydrocarbons but also ensure a low amount of side chains in the products; this is achieved by controlling the yield of C1–C4 components to no more than 4%. Additionally, the ratio of naphtha to diesel products should be 3:7, with the dew point of the diesel products being below -20°C. If too many side chains of the oil are broken during the open-loop cracking process, it not only affects the overall yield of the products but also undermines the advantage of diesel products having a low freezing point. Additionally, hydrogen consumption increases, which in turn impacts the economic viability of the entire project. Plan 1: Material Balance Table
Item, Material Name, Weight%, Kilograms/hour, 10,000 tons/year, Remarks
Input: Coal tar – 100, 12,500, 10, 8,000 hours; Hydrogen – 7, 875, 0.6, 10,000 Nm3/h; DMDS – 0.4, 50, 0.04; Sulfurizing agent. Total – 107.4, 13,425, 10.64
Output: H2S+NH3 – 1.34, 167.50, 0.134; Dry gas – 2.46, 307.50, 0.246; Naphtha – 18, 2,250.0, 1.80; Diesel – 59.87, 7,483.75, 5.987; Water – 5.49, 686.25, 0.549; Residual oil – 0.24, 30.00, 0.024; Coal tar pitch – 20, 2,500, 2.0. Total – 107.40, 13,425, 10.74
Under this plan, all quality indicators of the refined products are high; the yield of refined products is slightly low. A small amount of residual oil (heavy marine fuel oil) is discharged, along with asphalt as a by-product. Diesel products are high-grade finished goods with low freezing points and low sulfur and nitrogen content, and they command high prices in the market. (II) Option 2: Fluidized bed + fixed bed hydrogenation process. Key points: The entire fraction of coal tar is fed into the fluidized bed hydrogenation unit; the gasoline fractions produced are sent to the fixed bed hydrogenation unit for further refinement, while the heavier fractions are subjected to both hydrogenation and cracking processes to produce finished products. This plan is accompanied by a hydrogen production plant with a capacity of 13,000 Nm3/h. The asphaltene content in the full distillate of coal tar can reach around 50%, and with traditional processing methods, the liquid yield is only 76%. By using the fluidized bed processing technology of Shanghai Xinyou Energy Technology Co., Ltd. to lighten the gum and asphaltenes in coal tar, the liquid yield of the product can be increased to 90%~95%. After hydroprocessing of the full fraction of coal tar in a fluidized-bed hydrogenation reactor, more than 85% of the S, N, O, and metal components are removed, while the degree of lightening of the resinous and asphaltenic components exceeds 90%. The gasoline fraction obtained after reaction separation is fed into a fixed-bed refining hydrogenation reactor, where the S, N, O, and metal components in the fraction are effectively removed; at the same time, the olefins, dienes, and aromatics are saturated, resulting in naphtha components that meet the required standards. The heavy fractions produced by the fluidized bed are first filtered and pressurized before being fed into a fixed-bed refining + cracking reactor, where they undergo hydrocracking to break down larger molecules into smaller ones (naphtha, diesel fractions). After the cracking reaction, the resulting products are sent to a product distillation column for separation. In this process, the selectivity of the catalyst must not only enable the ring-opening and cracking of polycyclic and fused-ring hydrocarbons but also ensure a low amount of side chains in the products; this is achieved by controlling the yield of C1–C4 components to no more than 4%. Additionally, the ratio of naphtha to diesel products should be 3:8, with the dew point of the diesel product being below -20°C. If too many side chains of the oil are broken during the open-loop cracking process, it not only affects the overall yield of the products but also undermines the advantage of diesel products having a low freezing point. Additionally, hydrogen consumption increases, which in turn impacts the economic viability of the entire project. Material balance table for Option 2
Item, Material name, Weight%, Kilograms/hour, 10,000 tons/year, Remarks
Input: Coal tar – 100, 12,500, 10, 8,000 hours; Hydrogen – 9, 1,125, 0.9, 13,000 Nm3/h; DMDS – 0.3, 37.5, 0.03; Sulfurizing agent. Total – 109.3, 13,662.5, 10.93
Output: H2S+NH3 – 1.37, 171.25, 0.137; Dry gas – 5, 625.00, 0.50; Naphtha – 25.38, 3,172.5, 2.538; Diesel – 69.19, 8,468.75, 6.919; Water – 6.86, 857.5, 0.686; Residual oil – 1.5, 187.5, 0.15; Heavy marine fuel oil. Total – 109.3, 13,662.5, 10.93
The total investment for Option 1 is 308.99 million yuan, of which 305.7 million yuan is allocated to construction costs. The total investment for Option 2 is 291.7 million yuan, with 288.22 million yuan going towards construction costs.
Comparison of the options: Both options meet the requirements for project approval. However, Option 2 has advantages over Option 1, specifically: 1. It utilizes fluidized bed technology, which is a more advanced process that effectively addresses issues related to heat extraction, temperature elevation, and coking ； 2. Higher raw material conversion rate, converting coal tar pitch into high-quality, high-value gasoline and diesel ； 3. Ensure long-term continuous operation of the hydrogenation unit (more than 2 years for fluidized-bed hydrogenation, and 8–10 months for fixed-bed hydrogenation), reducing operational complexity and minimizing investment requirements ； 4. The catalyst is regenerated online, eliminating the need for shutdowns for loading and unloading, which facilitates stable, continuous, and efficient operation of the plant ； 5. It offers better economic benefits, simultaneously greatly improving the processing capacity of the device, resulting in even more significant potential advantages. The 150,000 tons/year fluidized-bed tar hydrogenation industrial plant was successfully commissioned in Huanghua, Hebei in August 2015, with the process operational and achieving ideal results.