Pressure Vessels 

Pressure Vessel: Introduction

It is necessary to apply pressure to a container in order to store liquids, vapors, or gases at pressures significantly higher or lower than the surrounding atmosphere. They are used in a wide variety of fields, from the petrochemical industry to the oil and gas business to the chemical industry to the food processing industry. Machines like reactors, flash drums, separators, and heat exchangers all make use of pressure vessels.

There is a codified set of rules and regulations that cover every aspect of pressure vessels. The Boiler and Pressure Vessel Code (BPVC) is the most frequently used and acknowledged collection of guidelines for boilers, pressure vessels, and nuclear power plant components. 

Pressure Vessel: How Does It Work?

In order for a pressure vessel to perform its intended purpose, it must first achieve the necessary level of pressure for the task at hand similar to how a diving tank must maintain its air pressure. Either directly, through the use of valves and release gauges, or indirectly, through the transfer of heat, they can deliver the pressure. 

Temperatures typically exceed 750 degrees Fahrenheit (400 degrees Celsius), and potential pressure levels range anywhere from 15 psi to to 150,000 psi. There is a wide range of capacities available for pressure tanks, ranging from 75 litres (about 20 gallons) to several thousand litres.

Pressure Vessels: Uses, Types

Different types of Pressure Vessels and Their uses 

1. Storage Vessels

These are pressure containers that are used to keep liquids, vapours, and gases for a temporary period of time. The container may be put to use later on in a subsequent process to hold fluids, or it may be used to store finished goods like compressed natural gas (CNG) and liquid nitrogen.

3. Packed bed reactor 

Cylindrical containers known as packed bed reactors house an immobilised bed of catalyst inside their interior. The reaction occurs on the surface of the solid catalyst as the gaseous or liquid reactants flow out of the vessel in one direction.

 The conversion rate of packed bed reactors is high relative to the amount of catalyst used, and there is a greater surface area of contact between the reactant and the catalyst. 

Having said that, the cylindrical vessel that houses these reactors needs to be strong enough to withstand the weight of the catalyst bed.

4. Jacked reactors 

During a chemical reaction, it is important to keep the temperature of the Pressure Vessels, products, and catalysts at the same level. The contents of the reactor can be cooled or heated by a utility fluid that circulates through the jacket that wraps around the vessel. Examples of such fluids include cooling water and steam.

When designing reactors, one of the most important factors to take into account is the type of the reaction. During a chemical reaction, heat can either be given off referred to as an exothermic reaction or taken in referred to as an endothermic reaction .

 It is necessary to either heat or cool the mixture during the reaction in order to create conditions that are favourable for the reaction, which will maximise product conversion and increase efficiency. Additionally, this will help prevent an uncontrolled increase or decrease in temperature during the reaction. Therefore, a reactor with a jacket is something that needs to be considered.

5. Fluidized bed reactor 

Additionally, it includes a bed of the catalyst. The solid catalyst is kept in suspension inside the   reactor pressure vessel by the high velocities at which the gaseous or liquid reactants move across the bed in these reactors.

 This causes the solid catalyst to operate more like a fluid. Because the catalyst is fluidized, it is possible to thoroughly mix the reactants in all directions. As a result, it is possible to achieve high reactant conversion and mass transfer rates as well as a temperature that is uniform throughout the reactor.

6. Spherical pressure vessels 

Due to the robust structure of spherical pressure vessels, they are ideally suited for the containment of high-pressure fluids; yet, the fabrication of these vessels is complicated and expensive. Because both the internal and external load are distributed uniformly around the surface of the sphere, there are no weak places in the structure.

 They have a lower surface area to volume ratio than the other options. If a pressure vessel of the same volume is going to be manufactured, then fabricating a spherical vessel will require a smaller amount of material than fabricating a cylindrical vessel. Because of its smaller surface area, the spherical vessel will experience a lower rate of heat transfer from the more intensely heated body in comparison to other shapes.

7. Cylindrical Pressure Vessels

A cylindrical shell and a set of heads are the component parts that make up a cylindrical pressure vessel. The body of the pressure vessel is represented by the cylindrical shell. The heads act as end caps or an enclosure for the shell, covering the contents of the vessel that they are attached to.

 The heads can have a more rounder or flatter contour, depending on your preference. This latter minimises the cylindrical vessel's susceptibility to damage.Because of their adaptability and space efficiency, cylindrical pressure vessels are the most common type of vessel. 

They can be manufactured at a far lower cost than spherical vessels can. However, in comparison to spherical pressure vessels, they tend to have a lower strength. In order to obtain the same level of strength as spherical vessels when bearing the same level of internal pressure, their walls often need to be thicker.

8. Boilers

A boiler is a type of heat transfer equipment that can draw its heat from a fuel source, a nuclear power source, or an electrical power source. Boilers are used in a variety of industries, including the chemical, nuclear, and electrical power industries.

 The majority of the time, they assume the shape of an enclosed vessel that performs the function of a conduit, allowing heat to travel from the source of heat to the fluid that is being heated.The heating of liquids is the primary function of these various devices. 

The fluid's phase will regularly transition from the liquid state, in which it is currently found, to the vapour state, in which it is currently found, inside the boiler. In addition to being used in the generation of electricity, the vapour that is created by the boiler is also put to use in a range of other applications that include heating.

The turbine blades are given a boost in speed by the pressurised steam that is generated by steam boilers. This steam is produced at a higher pressure than is typical. Because of this, the vessel that makes up the boiler needs to have a high degree of strength in order to be able to endure the extremely high pressures and levels of thermal stress that it will be subjected to. 

The majority of different kinds of substances experience a weakening of their level of strength as the temperature is raised.

9. Heat Exchangers

Heat exchangers are devices that are used to move heat from one fluid to another or between multiple fluids. They find widespread application in the energy, food processing, bioprocessing industries and pharmaceutical, among others.

 The functionality of heat exchanger equipment is reliant on the thermal and flow properties of the fluids that are participating in the heat exchange, as well as the thermal property of the conductive partition for indirect contact heat exchangers.

 The difference in temperature between the hot and cold fluids in a heat exchanger causes the materials in the device to be subjected to stress, as does the internal pressure of the device, which contains the fluids.

10. Process Vessels

These vessels are a second subcategory that can be derived from pressure vessels. In commercial environments, these containers are used for a wide variety of processes, including mixing, agitation, decanting, distilling, mass separating, and chemical reactions.

 The degree to which there will be a change in pressure inside the process vessel is determined by the process itself as well as the substances that are being changed.

11. Columns for Distillation

As a consequence of this, a mixture of liquids can be sorted into groups according to the particular degrees of volatility that they possess.

Vapours, and Storage and transport of liquids, gases at pressures much greater or lower than ambient pressure requires the use of pressure vessels. Some rules govern the design, building, repair, and testing of pressure vessels; examples are the ASME BPVC and API 510. Safety during operation of the pressure vessel is prioritised during the creation of such rules.

Heat exchangers, boilers, Storage tanks, and process vessels are the various types of pressure vessels. You can find both spherical and cylindrical pressure vessels. In most cases, vessels will be cylindrical in shape, but their tops may be hemispherical, ellipsoidal, or toroidal. A pressure vessel's axis might be either vertical or horizontal.

FAQ: Pressure Vessels
 

Q. What are pressure vessels used for?
Ans. Pressure vessels designed to maintain a pressure much higher or lower than that of the surrounding environment, in order to store or transport gases or liquids.
 

Q. What is a reaction vessel used for?
Ans. Reaction vessel is used for holding the components of a reaction.
 

Q. What is difference between vessel and reactor?
Ans. A vessel is a container for the steam or gases that power a turbine to generate energy, whereas a reactor is the Engine that generates the steam or hot gases.