Technical exchange on alkylated waste acid and subsequent regeneration systems

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The poster is involved in the sulfate alkylation process, which is the mainstream alkylation method used in China today, as well as in waste acid regeneration systems. Over the years of production experience, I have acquired some practical technical knowledge, which I would like to share with all the experts here in the hope of sparking discussion and fostering mutual improvement. The original poster has raised three questions: 1. In the sulfate-based alkylation process, propane is present in the coolant; typically, this substance is first washed with alkali before being fed into the dehydrogenation tower for separation, but practical analysis shows that this step is not necessary. 2. Alkylation waste acid contains a large amount of liquefied gas, accounting for about 1%-1.5% of its composition; most companies do not recycle this gas, or they use gas tanks for recovery, which incurs high costs. 3. Alkylation waste acid contains organic hydrocarbons such as isooctane, C5 compounds, ASO, sulfates, and other complex components, which account for about 12%-15% of its composition. Isooctane can be recovered, but it seems that companies do not carry out effective recovery processes, either because the cost of recovery is high. Below, an economic accounting sheet will be prepared to estimate the actual economic benefits. I. Overview of the sulfuric acid-based alkylation waste acid system engineering 1. Alkylation waste acid refers to the 90%-91% low-concentration sulfuric acid that is discharged from the bottom of the acid sedimentation tank in the alkylation unit, in order to maintain the acid concentration required for the alkylation reaction. 2. The process flow for alkylating waste acid involves transferring the waste acid to an acidic gas separation tank, and then pumping it to a waste acid regeneration unit using a waste acid pump. 3. Due to differences in process versions, some units discharge waste acid into a buffer tank, which is then pumped by a waste acid pump to the waste acid regeneration unit (this is the process used in our company). 4. The main components in alkylated waste acid include sulfuric acid, liquefied gas, and alkylated organic hydrocarbons; the content of liquefied gas is 1%-1.5%, while that of alkylated organic hydrocarbons is around 11%-15%. 5. The current mainstream treatment method for alkylated waste acid in China is to carry out high-temperature pyrolysis of the waste acid to regenerate concentrated sulfuric acid. II. Analysis of the actual operating conditions of the system file:///C:\Users\阿斯蒂芬\AppData\Local\Temp\ksohtml\wpsADB2.tmp.png 1. The liquefied gas discharged from the alkylation unit is released into the flare stack without any utilization; this constitutes a loss of materials. 2. It is a loss that the alkylation oil entrained in the waste acid from the alkylation unit is not recovered and instead is sent to the cracking furnace for incineration. 3. In waste acid, the alkylated organic hydrocarbons, without being extracted, continue to react within the waste acid to produce viscous substances similar to asphalt. This leads to fluctuations in the oxygen consumption of the waste acid regeneration equipment; in severe cases, it can cause blockages in the nozzles used for spraying waste acid into the cracking furnace. 4. The alkylated organic hydrocarbons in the waste acid are not recovered, which in turn exacerbates the clogging of the boiler tubes in the waste acid regeneration unit. III. Analysis of material losses during the actual operation of the system: Material losses are divided into losses of gaseous liquefied gas and losses of alkylation oil. The analysis is based on an annual production of 200,000 tons of isooctane from two reactors; the specific figures are as follows: 1. For an annual production of 200,000 tons of isooctane, the sulfuric acid consumption ranges from 80 to 110 KG per ton. The acid consumption calculated below is based on a total of 20,000 tons. 2. The content of liquefied acid in each ton of waste acid is 0.01–0.015 tons. 3. Amount of alkylated organic hydrocarbons per ton of waste acid: 0.11–0.15 tons. 4. Amount of liquefied gas carried in the waste acid: 20,000×0.01 (0.015) = 200 (300) tons. 5. Amount of alkylated organic hydrocarbons: 20,000×0.11 (0.15) = 2,200 (3,000) tons. IV. Materials that can be recovered after technical improvements to the system: 1. 90% of the liquefied gas present in the waste acid can be recovered. 2. The alkylated organic hydrocarbons in waste acid consist of components such as isooctane, sulfates, and ASO; among these, light components like isooctane can be recovered. The amount of oil that can be recycled accounts for about 15% of the total alkylated organic hydrocarbons. Range: Minimum/Maximum quantity of material, Average value, Recyclability rate, Recyclable amount, Price (yuan), Total (yuan). Liquefied gas (tons): 200t, 300t, 250t; Recyclability rate: 90%; Amount to be recycled: 225t; Price: 2850; Total: 641250. Alkylated organic hydrocarbons (tons): 2200t, 3000t, 2600t; Recyclability rate: 15%; Amount to be recycled: 390t; Price: 4350; Total: 1696500. V. Calculation of costs for system technical improvements and operating costs: 1. Modifications are required based on the current process pipelines and equipment; one DN100 sight glass needs to be added, as well as some elbows and pipelines (the exact quantities will be determined through negotiation, and the costs will be calculated later). 2. Operation: Add two existing centrifugal pumps with capacities of 15KW and 22KW. 3. Extended pump operation time: about 2 hours per day. 4. Cost calculation: (15+22)×2×333 days×0.75 yuan = 18,481.5 yuan per year. VI. Remaining profit: 641,250 + 1,696,500 – 18,481.5 = 2,319,268.5 yuan per year. VII. The above represents a preliminary calculation of the costs; due to differences in the operating conditions of the equipment as well as variations in the impurity components present in the raw materials, the amount of liquefied gas and oil carried along with the waste acid produced during alkylation will vary to some extent. Notes: 1. The above calculation is based on an annual production of 20,000 tons of waste acid; if the processing capacity of the facility is less than 20,000 tons, the costs will still be calculated using the same method. In an effort to stimulate further discussion, I invite all experts and professionals to share their insights so that we can exchange ideas and explore ways to maximize the company’s economic efficiency.