Undoubtedly, oil and gas play a vital role in the contemporary human society. As these exhaustible natural resources continue to be utilized, the level of competition in this sector has intensified.
HFM has demonstrated its commitment to enhancing energy efficiency for our oil and gas associates through our custom-designed solutions, including oil heat exchanger and gas heat exchanger. These plate heat exchangers for oil and gas applications are engineered to facilitate optimal heat transfer between fluids, resulting in superior yield results and cost reduction for our partners in the oil and gas industry.
A heat exchanger is an equipment designed to transfer heat efficiently between two different mediums, which can either be in direct contact or separated by a solid wall to prevent mixing. This device finds wide applications in various industries, including space heating, refrigeration, air conditioning, power generation, chemical, petrochemical, natural gas processing, and sewage treatment.
The petroleum refining industry is a classic example of the utilization of heat exchangers. In this industry, crude oil is refined using fractional distillation to produce more useful petroleum products like gasoline, diesel fuel, heating oil, kerosene, asphalt base, and liquefied petroleum gas.
The separation of components of crude oil can be achieved by utilizing the differences in their boiling points. The process of fractional distillation involves heating the crude oil to vaporize it and then condensing the vapor at different levels of the distillation tower, depending on their boiling points. The resulting products are called fractions.
Heat exchangers play a crucial role in the preheating of feedstock in distillation towers and refinery processes, ensuring that they reach the required reaction temperatures. Heat exchangers use either steam or hot hydrocarbon transferred from other parts of the process as heat input. A fraction obtained from crude oil can be classified into two categories: Refined Products and Petrochemical Products.
Refined Products are fractions containing a variety of individual hydrocarbons, including gasoline, asphalt, waxes, and lubricants. On the other hand, Petrochemical Products are fractions consisting of one or two specific hydrocarbons of high purity, such as benzene, toluene, and ethylene.
2. Atmospheric distillation tower
3. Vacuum distillation tower
4. Heat exchangers, coolers, and process heaters
5. Tank storage
6. Heater and boiler
7. Gas and air compressor
9. Pumps, piping and valves
1. Desalination/ Desalting
2. Atmospheric Distillation/ Crude Oil Distillation
3. Vacuum Distillation
5. Thermal Cracking
The refining of crude oil entails a series of intricate stages to yield valuable resources. These stages comprise desalination in desalters, atmospheric distillation in crude distillation unit (CDU), vacuum distillation in Vacuum Distillation Unit (VDU), and others.
Of particular importance among these processes is the utilization of oil heat exchangers and gas heat exchanger, to facilitate the heating or cooling of the mixture to their optimum temperature, enabling the chemical reactions to occur efficiently.
Crude oil often contains water, inorganic salts, suspended solids, and water-soluble trace metals. To reduce corrosion, plugging, and fouling of equipment these contaminants must be removed by desalting (dehydration). This is done in desalters.
Crude oil must first be desalted, by heating to a temperature of 100-150 °C and mixing with 4-10% fresh water to remove inorganic salts (primarily sodium chloride). If these salts and heavy metals are not removed, they can form acids when heated, causing corrosion of downstream process equipment. Salts can also form deposits, causing plugging of heat exchangers or clogging trays in process towers. Crude oil exits from the desalter at temperature of 250 °C–260 °C.
Atmospheric distillation or the crude distillation is the first and most fundamental step in the the refining process. The primary purpose of the atmospheric distillation tower is to separate crude oil into its components (or distillation fractions) for further processing by other processing units.
Atmospheric distillation typically sets the capacity limit for the entire refinery. All crude oil processed must first go through atmospheric distillation. Also, atmospheric distillation typically provides most of the feed for the other process units in the refinery.
Following the desalter, the crude oil is further heated by exchanging heat with some of the hot, distilled fractions and other streams. It is then heated in a fuel-fired furnace (fired heater) to a temperature of about 398 °C and routed into the bottom of the distillation unit.
The heated crude is injected into the lower part of the distillation column, where much of it vaporizes. As the vapors rise through the tower, they pass through a series of perforated trays or structured packing.
The vapors from the top of the column are a mixture of hydrocarbon gases and naphtha, at a temperature of 120 °C–130 °C. The fractions removed from the side of the distillation column at various points between the column top and bottom are called sidecuts. Each of the sidecuts (i.e., the kerosene, light gas oil, and heavy gas oil) is cooled by exchanging heat with the incoming crude oil.
All the fractions (i.e., the overhead naphtha, the sidecuts, and the bottom residue) are sent to intermediate storage tanks before being processed further. The vapor stream associated with steam used at bottom of the column is condensed by the water cooler and the liquid collected in a vessel is known as reflux drum which is present at the top of the column. The cooling and condensing of the distillation tower overhead is provided partially by exchanging heat with the incoming crude oil and partially by either an air-cooled or water-cooled condenser.
Some part of the liquid is returned to the top plate of the column as overhead reflux, and the remaining liquid is sent to a stabilizer column which separates gases from liquid naphtha. A few plates below the top plate, the kerosene is obtained as product at a temperature of 190 °C–200 °C. Part of this fraction is returned to the column after it is cooled by a heat exchanger.
This cooled liquid is known as circulating reflux to contact with the rising vapors, helping to cool them. This effect of counter-current flows of rising vapors meeting falling cooler liquids allows equilibrium conditions to be established throughout the column. The lighter (less-dense) hydrocarbons will condense at higher points in the distillation tower, heavier hydrocarbons will condenser lower down.
This results in separation of the hydrocarbons based on the different temperatures at which they boil/condense. Hydrocarbons are drawn off the tower at different heights to get a set of streams of different boiling points. These different streams are called distillation cuts or fractions. These individual streams are then sent to other units for further processing or to finished product blending.
The remaining crude oil is passed through a side stripper which uses steam to separate kerosene. The kerosene obtained is cooled and collected in a storage tank as raw kerosene, known as straight run kerosene, that boils at a range of 140 °C–270 °C. A few plates below the kerosene draw plate, the diesel fraction is obtained at a temperature of 280 °C–300 °C. The diesel fraction is then cooled and stored.
The top product from the atmospheric distillation column is a mixture of hydrocarbon gases, e.g., methane, ethane, propane, butane, and naphtha vapours. Residual oil present at the bottom of the column is known as reduced crude oil (RCO). The temperature of the stream at the bottom is 340 °C–350 °C, which is below the cracking temperature of oil.
The pressure at the top of the distillation tower is maintained at 1.2–1.5 atm so that the distillation can be carried out at close to atmospheric pressure, and therefore it is known as atmospheric distillation column. In most refineries, the bottoms from the atmospheric distillation tower will be sent to the vacuum tower for further separation.
The fundamental purpose of the atmospheric tower is to separate fractions with boiling points lower than 350 ℃, including but not limited to gas, coal, and diesel. The atmospheric tower has a specific dimension of f6000x45335mm and is designed to feature a composite hole miniature fixed valve tray within its internal components. The tower comprises a total of 48 layers of trays, five of which belong to the stripping section.
Crude oil is a highly viscous substance, and its viscosity may lead to fouling and scaling on the heat transfer surfaces. To mitigate this, heat exchangers with plates that feature deep grooves are utilized to enhance heat transfer and minimize fouling.
Furthermore, temperature instability is a common challenge encountered in chemical processes, and heat exchangers must be designed to handle such conditions. In situations where the chemical system temperature is expected to exceed 100℃, a fully-welded type heat exchanger is typically used.
This type of heat exchanger is designed to withstand high pressure and temperature and minimize the risk of leaks or failures. On the other hand, detachable plate heat exchangers with EPDM gaskets are a better option for lower temperatures, as they are more cost-effective and offer ease of maintenance.
In summary, heat exchangers are essential components of the oil refining process, and their proper selection and design are crucial to ensure efficient and safe operations. The type of heat exchanger utilized depends on the specific characteristics of the crude oil and the chemical system, including viscosity, temperature, and pressure.
|Physical properties||Density/ ρ(kg/m³)||Heat Capacity/ C(KJ/(kg·℃)||Viscosity/ μ(Pa·s)||Thermal Conductivity/ λ(W/(m·K)|
Petroleum crude oil is a complex mixture of hundreds of different hydrocarbon compounds having from 3 to 60 carbon atoms per molecule, although there may be small amounts of hydrocarbons outside that range. The crude oil refining begins with distilling the incoming crude oil using atmospheric distillation operating at pressures slightly above atmospheric pressure.
In distilling the crude oil, it is important not to subject the crude oil to temperatures above 370 to 380 °C because the high molecular weight components in the crude oil will undergo thermal cracking and form petroleum coke at temperatures above that.
Formation of coke would result in plugging the tubes in the furnace that heats the feed stream to the crude oil distillation column. Plugging would also occur in the piping from the furnace to the distillation column as well as in the column itself.
The constraint imposed by limiting the column inlet crude oil to a temperature of more than 370 to 380 °C yields a residual oil from the bottom of the atmospheric distillation column consisting entirely of hydrocarbons that boil above 370 to 380 °C.
To further distilling the residual oil from the atmospheric distillation column, the distillation must be performed at absolute pressures as low as 10 to 40 mmHg (also referred to as Torr) to limit the operating temperature to less than 370 to 380 °C.
The primary advantage of vacuum distillation is that it allows for distilling heavier materials at lower temperatures than those that would be required at atmospheric pressure, thus avoiding thermal cracking of the components. Firing conditions in the furnace are adjusted so that oil temperatures usually do not exceed 380°C (716 °F).
Heavy distillates produced during the vacuum distillation process include light gas oil and heavy gas oil, which are then sent to the downstream separation and conversion units to be further refined into lube oil base stocks, or as feedstock for hydrocracking to produce light and middle distillates, such as jet fuel, kerosene, and diesel. Vacuum tower equipped with three padding sections, three layers of the oil sump tank, three combined liquid distributors, and metal mellapale packing on the first two layers and metal intalox saddle in the under layer.
The first vacuum side stream is exhausted from the first layer of the oil sump tank and cooled down to 80℃ after heat exchange, some of which flows out as product and some of which returns to the upper part of the first padding section as vacuum overhead reflux oil after being cooled down to 40℃ by the condenser.
The second vacuum side stream is exhausted from the second layer of the oil sump tank, one line of which is cooled down to 80℃ after heat exchange and flows out as a product, one of which returns to the upper part of the second padding section as vacuum overhead reflux oil and the other of which returns to the upper part of the third padding section as light wash oil with no need to be cooled.
Excess vaporization oil (third vacuum side stream) is exhausted from the third layer of the oil sump tank, some of which returns to the upper part of the third padding section as heavy wash oil, some of which mixes with the second vacuum side stream, enters into the integrated heavy oil line which is cooled down to 80℃ after heat exchange and flows out as product. Any residual oil leftover in the vacuum distillation column is transferred to the coker unit for further refining.
The 10 to 40 mmHg absolute pressure in a vacuum distillation column increases the volume of vapor formed per volume of liquid distilled. The result is that such columns have very large diameters.
Distillation columns may have diameters of 15 meters or more, heights ranging up to about 50 meters, and feed rates ranging up to about 25,400 cubic meters per day (160,000 barrels per day).
The vacuum distillation column internals must provide good vapor-liquid contacting while, at the same time, maintaining a very low pressure increase from the top of the column top to the bottom. Therefore, the vacuum column uses distillation trays only where withdrawing products from the side of the column (referred to as side draws).
Most of the column uses packing material for the vapor-liquid contacting because such packing has a lower pressure drop than distillation trays. This packing material can be either structured sheet metal or randomly dumped packing such as Raschig rings or other packing materials.
On the process mentioned above, there is a few oil heat exchanger application throughout the oil refining process.
Crude heat exchanger before desalination: crude oil of about 20-45 ℃ flows into the heat exchanger and then into the electrical desalter after being heated up to 100-150 ℃.
Crude heat exchanger after desalination: desalted crude oil flows into the primary tower after heating up to 220-240℃.
Primary distilled oil heat exchanger: After primary distillation, the oil flows into the heat exchanger and is heated to 270-280 ℃.
Primary overhead oil heat exchanger: the overhead oil gas is cooled down to 40℃ after passing through the overhead hot-water heat exchanger and air cooler and flows into the overhead reflux tank.
Overhead oil gas heat exchanger: the oil gas from the atmospheric overhead enters the return tank (Volume-103) for oil-water separation after cooling to 70 ℃ by the air cooler.
Overhead oil-water cooler: Non-condensable oil gas is cooled down to 40 ℃ by the condenser after entering the overhead product tank for oil-water separation.
First-line oil heat exchanger: the primary distilled oil, which is heated up to 370-380 ℃ by the atmosphere furnace, flows into the first-line oil heat exchanger and is cooled down to 45℃.
Second-line oil heat exchanger: the primary distilled oil, which is heated up to 370-380 ℃ by the atmosphere furnace, flows into the second-line oil heat exchanger and is cooled down to 60-70℃.
Third-line oil heat exchanger: the primary distilled oil, which is heated up to 370-380 ℃ by the atmosphere furnace, flows into the third-line oil heat exchanger and is cooled down to 70℃.
First vacuum side stream heat exchanger: first vacuum side stream is exhausted from the first layer of the oil sump tank and cooled down to 80℃ after heat exchange, some of which flows out as product and some of which returns to the upper part of the first padding section as vacuum overhead reflux oil after being cooled down to 40℃ by the condenser.
Second vacuum side stream heat exchanger: second vacuum side stream is exhausted from the second layer of the oil sump tank, one line of which is cooled down to 80℃ after heat exchange and flows out as a product, one of which returns to the upper part of the second padding section as vacuum overhead reflux oil and the other of which returns to the upper part of the third padding section as light wash oil with no need to be cooled.
Third vacuum side stream heat exchanger: third vacuum side stream mixes with the second vacuum side stream, enters into the integrated heavy oil line, which is cooled down to 80℃ after heat exchange and flows out as a product.
The vacuum residual oil heat exchanger: the vacuum residual oil is extracted from the bottom of the vacuum tower by the pump after it is cooled to 120 ℃, one of which flows out, one of which mixes with the second and third vacuum side stream into the integrated heavy oil line and flows out.
According to a report released by the World Economic Forum, almost 50% of industrial energy input is wasted, and waste heat recovery presents an effective solution for addressing this issue. As highlighted in a report by the US Department of Industry, recovered heat can be utilized for generating electricity, heating and absorption cooling.
In this process, heat exchangers play a critical role in preheating air before it enters the furnace system, thereby reducing the fuel consumption and energy usage of the furnace. To achieve an ideal energy triangle, large industries such as oil and gas are proactively exploring ways to balance energy security, energy affordability, and environmental sustainability by embracing eco-friendly practices.
At HFM, we are proud to offer effective and reliable solutions for oil and gas heat exchanger needs. With our proven track record of delivering high-performance and energy-efficient heat exchangers, we have become a trusted name in the industry. Our team of experienced engineers and technicians work closely with you to identify the optimal solution that meets your specific requirements.
If you are looking to enhance your energy efficiency and minimize energy costs, reach out to us today to learn more about our range of plate heat exchangers and how they can benefit your operations.