1. Crude Oil Gasoline & Diesel Refining Plant Equipment

Petroleum extracted directly from oil wells without processing is customarily called crude oil. It is a dark brown or dark green viscous liquid or semi-solid combustible substance composed of various hydrocarbons.

Crude oil contains a wide variety of hydrocarbons. Petroleum refining separates each component for further utilization. Chemists carry out petroleum refining via the following procedures:

1. The classic and widely adopted method to separate different components (known as fractions) from crude oil relies on differences in boiling points, a process termed fractional distillation. The basic principle is heating crude oil to vaporize it, then liquefying the generated vapor.

2. Newer technologies apply chemical processing to certain fractions to produce other fractions, which is referred to as conversion.

The atmospheric-vacuum distillation unit serves as the core front-end facility for crude oil processing. It separates crude oil into products with various boiling point ranges and feedstocks for secondary processing.

I. Process Overview

The atmospheric-vacuum distillation unit is the primary processing step in oil refining. Crude oil is separated via distillation into multiple oil products and feedstocks for downstream processing units. The control system performance and operation proficiency of the atmospheric-vacuum distillation unit exert a critical impact on refinery product quality, yield rate and efficient utilization of crude oil. The process can be divided into the following sections:

1. Electric Desalting

Electric desalting involves injecting a certain volume of low-chloride fresh water or overhead condensed water from the atmospheric tower into crude oil. Thorough mixing dissolves salts remaining in crude oil while diluting the original oil-water mixture to form a new emulsion. Under the effect of demulsifiers, sedimentation and separation take place to achieve desalting.

2. Crude Oil Distillation

A. Crude oil distillation units in China are generally equipped with a pre-fractionator or flash tower upstream of the atmospheric fractionating tower. This setup promptly strips light oil vaporized during crude oil heat exchange, preventing it from entering the atmospheric heating furnace. It reduces the heat load of the heating furnace and pressure drop of the crude oil heat exchange system, thereby cutting down unit energy consumption and operating costs. Light gasoline fractions from the pre-fractionator overhead serve as feedstock for catalytic reforming.

B. The atmospheric tower is fitted with 3 to 4 side draws to manufacture products or blending components including gasoline, solvent oil, kerosene, aviation kerosene, light diesel oil and heavy diesel oil.

C. Side draws from the vacuum tower supply feedstock for catalytic cracking or hydrocracking. The product composition is relatively simple with low requirements for fractionation precision.

D. Vacuum towers normally operate under wet or dry conditions, meaning little or no steam is injected into vacuum tower sections and vacuum furnace tubes.

3. Fractionating Tower

The fractionating tower is the core equipment in crude oil distillation. Key process parameters include tower temperature, pressure and reflux ratio. The flash pressure of the tower is determined by overhead pressure and total pressure drop of trays above the flash zone. Atmospheric tower pressure is governed by the overhead condensation system, while vacuum tower overhead pressure mainly depends on the capacity of vacuum ejectors. Lower flash pressure in both atmospheric and vacuum towers allows a reduced furnace outlet temperature at the same vaporization rate, cutting fuel consumption. Reduced pressure in sections above the flash zone increases relative volatility between side draw fractions and facilitates their separation. Optimization control is primarily implemented around the atmospheric tower.

4. Heating Furnace

For crude oil distillation heating furnaces, the maximum oil temperature inside furnace tubes under the specified vaporization rate must stay below the oil cracking temperature (especially for vacuum heating furnaces). From an equipment perspective, furnace tube expansion is adopted in vaporization zones to cap the peak crude oil temperature inside tubes at 400°C.

II. Impacts of Control System Selection on Process Benefits

Prior to the 1980s, conventional instrument control dominated the traditional petrochemical industry. Distributed Control System (DCS) was gradually adopted starting from the 1990s. Replacing conventional instruments, DCS greatly boosted the petrochemical industry in three aspects:

1. DCS features internal wiring architecture, eliminating massive intermediate terminals and panel-mounted instruments to reduce failure points and deliver more reliable automatic control for production processes.

2. Powerful built-in software enables convenient configuration of complex control loops to realize intelligent and optimized control.

3. Its network function allows management staff to monitor real-time production status and utilize various management software to guide production efficiently.Below is the configuration introduction tailored for our 50,000–1,000,000 tons/year atmospheric-vacuum distillation units.

III. System Configuration

The system consists of field instruments, control stations, operator stations and an engineer station. Operator stations and the engineer station exchange data with control stations via the System Network (SNET), while real-time data transmission inside control stations relies on the Control Network (CNET).Typical scale: 70–100 control loops, 240–300 process detection points; 3–4 screen-based operating consoles allocated by work positions.

Basic Configuration

• 1 set of control station (1:1 redundant control panels)

• 3 operator stations (expandable on demand)

• 1 engineer station

• 7 industrial standard cabinets

• 52 I/O cards: 26 control I/O cards, 26 digital/analog input & output cards, all configured with 1:1 redundancy

• Power modules: supply redundant 24 V DC / 6 A and 5 V DC / 7 A direct current powerAuxiliary equipment: configured as required.

IV. Typical Control Functions

The crude oil distillation process is essentially a physical gas-liquid phase transition, so all control logics comply with fundamental principles of material balance, heat balance, phase equilibrium, mass transfer and heat transfer.

1. Balanced control of outlet temperatures of heating furnace branches

2. Heating furnace combustion control

3. Closed-loop quality control for fractionating towers

4. Multivariable intelligent control of atmospheric tower

5. Overflash rate control

Automating atmospheric-vacuum distillation units with DCS generates remarkable economic and social benefits in two dimensions:First, intelligent and complex control improves product quality and light oil recovery yield.Second, DCS replaces conventional instruments to lower intermediate failure rates, extend safe equipment operation cycles, reduce unplanned shutdowns and increase effective production time, creating additional economic gains.

Our Advantages

1. Optimized process flow and operation schemes.

2. With in-depth expertise in energy conservation and emission reduction, we deliver superior solutions and proprietary supporting facilities, reflected in: complete wastewater recovery, maximum heat recovery from side draw streams, variable frequency energy saving for pumps, uniquely designed heating furnaces, enhanced flue gas recovery, and optimized burners & soot blowers. These improvements drastically raise thermal efficiency up to 90% for crude oil processing.

3. Advanced distributed control system.