Resolving bottlenecks in increasing the capacity of the 100th distillation unit of Abadan Refinery

Master thesis

Trend of energy systems

Abstract

Crude oil distillation unit is one of the most important and critical operational units of any refinery. This unit often requires revision in the design of the structure (Revamping) or making small changes in its existing condition without the need to reduce or increase the basic devices of the process (Retrofitting) in order to achieve higher capacity, more extraction of the desired products, higher quality and usually more economic profit.  Removing the limitations and removing the bottleneck from the existing capabilities is usually the most common method to achieve the above goals by accepting the least risk.

The first step in all projects to increase the capacity is to identify the capabilities and limitations of the existing system. In this project, the following basic limitations were identified:

Heat recovery power from circulating kerosene (Kerosene Pump Around Duty)

Flooding phenomenon in the atmospheric distillation tower

Heat power of the furnace

then by applying The advanced distillation method and installation of a pre-separation tower instead of the Pre-flash Drum container made it possible to solve the mentioned limitations.

The analysis of the contents was done by simulating the existing unit and the results were worthy of attention. The limitations mentioned above have been removed, the possibility of increasing the capacity has been achieved. The economic benefits resulting from it are also significant.

Key words: crude oil distillation, capacity increase, crude oil preheating, advanced distillation, pre-separation tower

        When a refining company decides to increase its capacity, naturally, the first unit that must be evaluated is the distillation unit or so-called (Topping Unit). Trying to remove the bottlenecks from existing facilities and capabilities, which is often called Retrofit Design, is the cheapest and fastest way to achieve higher production capacities by accepting the least risk. The rise in the price of petroleum products and the consequent increase in energy costs due to political and international developments caused the industrialized countries, which are the largest energy consumers in the world, to make many efforts to optimize the oil and gas industries. Do petrochemicals, which are the largest and most consuming industries in terms of energy consumption. The results of these efforts are mainly expressed in the following two ways:

Reduction of energy consumption by the method of optimal use of energy in the industrial unit under discussion

Revision in the design and structure of petroleum and petrochemical units

Usually, in the first method, there is no need to make fundamental changes in the structure of the unit, so the costs incurred will be minimal. . While in the second method, it is often necessary to make a series of changes to achieve the desired goal. Then we will discuss the description of progressive distillation and possible methods for its application (in distillation unit 100 of Abadan refinery). Then, we will compare different process conditions and energy consumption in two normal and advanced distillation modes by simulating. Also, a brief explanation will be given regarding the simulation and how to do it for the discussed unit. These devices are used to separate crude oil by distillation into components according to their boiling point, so that the feed sources of each of the subsequent processing units are prepared according to their required characteristics.In order to achieve higher yields and lower costs, the separation of crude oil takes place in two stages:

The first stage is the separation of all crude oil into parts at atmospheric pressure

The second stage is sending the slow boiling residue of the first stage to another separation device that operates under high vacuum.

         from the vacuum distillation device , is used to separate the heavier part of crude oil into different components, because the high temperature required to evaporate this heavy part at atmospheric pressure causes its thermal cracking, which itself causes waste from dry gas production, as well as changing the color of the product and clogging the equipment due to coke production. Crude

         If the salt in the crude oil is more than 10 lb/1000 bbl (in terms of NaCl amount), the crude oil must be desalinated to prevent crusting and corrosion due to salt in the heat transfer surfaces and also the production of acids through the decomposition of chlorine salts. In addition, some metals that are water-soluble inorganic compounds that emulsify with crude oil and cause the deactivation of the catalyst in catalytic processing units are also removed in the desalination process. The standard used for desalination of crude oil until recent years was the presence of 10 lb of salt or more (in terms of NaCl) in 1000 bbl of crude oil. But now many companies desalinate all crude oil. In the justification of this additional action, it is mentioned that the reduction of crusting and corrosion of the devices and the increase of the life of the catalyst are mentioned. If the amount of crude oil salt is more than 20 pounds per thousand barrels, two-stage desalination is used, and in some cases the residues are processed by catalytic method, for some crude oils, three-stage desalination is used. The basis of the crude oil desalination method is to wash the existing salt with water. Here, there are issues in the effective and economical mixing of water and oil, as well as the moistening of suspended solid particles with water and the separation of washing water from oil. pH, density and viscosity of crude oil as well as the ratio of the volume of washing water to the volume of crude oil are effective in the ease of separation and efficiency. The second important goal of desalination is to remove suspended solids in crude oil. These materials usually include: fine particles of sand, clay, soil and particles of iron oxide and iron sulfide separated from pipelines, tanks and tankers, and other polluting sources, which enter crude oil during the transportation or exploitation stage.  60% or even 80% of all suspended solid particles larger than 0.8 microns must be removed. Desalination is done by mixing crude oil with 3 to 10% water by volume, at temperatures of 90 to 150 degrees Celsius. The ratio of water to crude oil and the temperature of this operation are functions of the density of crude oil.

(Tables are available in the main file)

Abstract

Crude distillation is one of the central and critical operating processes in a petroleum refinery and often revamping or retrofitting of the atmospheric column is necessary to increase throughput, fractionation, product yield and quality and, ultimately, profit. Existing facility debottlenecking is an attractive method for increasing production with a minimum risk.

The aim of this work is to examine and to show the effect of adding a prefractionator tower at the upstream of the atmospheric tower of on the energy conditions of the unit.

Preflash column is a distillation tray tower. It operates at around 180-200 Deg C with 4 barg top pressure. Located in Crude preheat train at a place where Crude is likely to reach about 180-200 Deg C, it separates water vapor, LPG and Naphtha fractions from the Crude as products.