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What is a Temperature Control Valve? It’s Working, Applications, and Types

Written by Anup Kumar Dey in Instrumentation

The temperature control valve is one of the most commonly used control valves. These valves are used in different industrial applications to control the temperature of the fluid. The efficient working of this valve is very important to achieve optimum efficiency. This article mainly explains the temperature control valve working, applications, and types.

What is a Temperature Control Valve?

A temperature control valve (TCV) is used to control the process temperature by regulating the flow or pressure of thermal fluid in a heating coil, tank shell, compressor, or other heating element. The temperature control valve is also known as a temperature regulator.

The temperature control valves are employed in processes that need to maintain a stable temperature when the ambient temperature changes.

The TCVs are useful in industrial, marine, and process control applications where liquids are diverted or mixed to attain the best operating temperature. They can also be used in a cogeneration system to regulate the temperature of the heat recovery loop to maximize heat recovery and ensure proper engine cooling. All of this helps to deliver the optimal temperature for your process and avoid costly downtime.

Valves for various applications are most commonly named by the number of their ports. For example, as the name suggests, a two-way valve contains two ports. A three-way valve contains three ports. A valve port is a valve connection point where fluids enter or exit the valve.

Sometimes, TCV can be used to moderate engine temperatures and a faulty TCV can even create the failure of car engines as suggested by some car accident attorneys.

How does a Temperature Control Valve Work?

Before delving into the workings of temperature control valves, it is vital to understand their design. The design of the temperature control valve consists of 4 major components parts:

  • Temperature sensing element
  • Sensor
  • Power supply
  • Controlling medium

The temperature-sensing element is responsible for sending a mechanical or electrical signal to an actuator. With this signal, the actuator then acts on a voltage supply that measures the position of the valve.

The temperature regulator is actuated by a mechanical temperature gauge. It contains a full lightbulb as the temperature sensor. Due to the thermal expansion properties of the material, it swells as the temperature rises. This expansion loads the actuator pressure. This pressure controls the valve position in the regulator that regulates the flow of refrigerant.

Temperature control valves use the following two common temperature control schemes:

Mixing of hot and cold process liquids:

In this case, the cold and hot process liquids are set at two dissimilar temperatures (Tx and Ty). A temperature control valve (TCV) is configured to physically mix these fluids to achieve the desired temperature. It is vital to observe that no chemical reactions take place between the liquids. The sensor installs in the hot process liquid. Ty calculates the thermal process fluid temperature and transfers it to the controller with the Tx setpoint. When the thermal process fluid temperature exceeds Ty, the controller recognizes the temperature change. The control valve mixes the cold process liquid with the hot process liquid until the desired temperature is gained.

Heat exchange between hot and cold process liquids:

In this process, instead of mixing the liquids, energy is transferred between two hot and cold process liquids. This means that the hot fluid flows through the heat exchanger shell while the cold fluid transfers energy through the tubes. The hot liquid transfers energy to the cold liquid and the temperature rise of the cold liquid is observed and regulated by a temperature transmitter and transferred to the temperature controller. As the temperature rises, the controller sends it to the temperature control valve to turn it on or off accordingly. It stays on until the desired temperature is reached, facilitating energy transfer.

Types of Temperature Control Valves

Broadly there are two types of temperature control valves;

  • Thermostatic Control Valves, and
  • Actuated Control Valves

Thermostatic Control Valves

Valves that work by detecting and regulating the temperature of the liquid inside are called thermostatic control valves. This temperature control valve is self-contained and requires no external power supply. The working temperature range is measured by the chemistry of the wax material and is preset at the factory or local dealer as recommended by the engine or equipment manufacturer.

When the thermostatic element is adjusted according to the specific temperature, it can’t be reformed without installing a new element. This rugged yet simple design stops operators from accidentally overheating or overcooling equipment, resulting in poor fuel economy, costly repairs, and downtime.

Actuated Control Valves

Unlike internal sensing valves, actuation control valves are typically part of a complete system that uses an external probe to sense temperature changes. The probe transfers a signal to the powertrain control module (PCM) to open and close the valve port using an external power supply. Normal system types include pneumatic, electric, or a combination of both.

However, this type of valve requires more components to function, it has several advantages. First, it tends to be more precise. So, if your application needs accurate temperature control, this method is the best option. Second, unlike a thermostatic valve, the actuated control valve permits flexible adjustments to the temperature range as operating conditions change.

Temperature Control Valve Applications

The temperature control valves are most commonly used for different industrial and residential applications. The following are the major applications of temperature control valves:

  • Unit heaters
  • Small jacketed pans
  • Small heater batteries
  • Tracer lines
  • Ironers
  • Small storage calorifiers
  • Small tanks
  • Acid baths

Some of the industries that use temperature control valves are

  • Food Industries
  • Oil and Gas sectors
  • Chemical and Petrochemical industries.

Advantages and Disadvantages of Temperature Control Valve

Advantages of Temperature Control Valve

  • These types of valves have low cost.
  • They have small sizes.
  • They are easy to install.
  • The temperature control valve has one trade installation.
  • It is very robust and reliable.
  • Tolerant of imperfect steam conditions and of being oversized.
  • It works on a self-acting principle which means that no external power is needed.
  • You can easily select it according to your requirements.
  • These valves are available in different designs different capillary lengths and temperature ranges.

Disadvantages of Temperature Control Valve

  • These valves are available in limited sizes.
  • They have limited pressure ratings.
  • Sensors tend to be much larger than the pneumatic and electronic equivalents and also much slower acting.
  • Limited turndown.

Follow this to learn the sizing of control valves.

What is PSSR or Pre-Startup Safety Review?

Written by Anup Kumar Dey in Health & Safety

The full form of PSSR is Pre-Startup Safety Review. It is an important element of the process safety management program. For chemical, petrochemical, oil and gas industries, safety is very important as they handle highly hazardous fluids. Pre-startup safety review or PSSR provides a final check prior to the commissioning of the processing facility to ensure that all the design and construction aspects are in order and it is safe to introduce the hazardous chemical into the system. In this article, we will explore more about PSSR; its purpose, importance, and process.

What is Pre-Startup Safety Review or PSSR?

A PSSR or pre-startup safety review is a systematic and thorough check of the plant and process to ensure safety and efficacy before bringing the system into operating mode. All new and modified facilities where any change modifies the process safety information should pass through this crucial process safety management review cycle. Agencies like OSHA (Occupational Safety & Health Administration), EPA (Environmental Protection Agency), etc require that all organizations must conduct PSSR before commissioning the plant to confirm that the plant is ready for start-up.

Pre Startup Safety Review should cover a review of all equipment, operating, maintenance, emergency procedures, and training. PSSR confirms that all appropriate elements of process safety management have been satisfactorily addressed.

In general, the PSSR for any project is usually one. However, some projects may require a number of PSSRs if the different process and utility modules are commissioned at different stages. PSSR is usually associated with the safe handover of the project from construction completion to the plant operation team.

In general, a PSSR must be performed before the startup of all the following circumstances:

  • Equipment modification.
  • Installation or change of new valves.
  • Addition of new control system/modification.
  • New feedstock or catalyst.
  • A new type of reactor or process vessel.
  • Capital projects.
  • Startup after an emergency shutdown
  • Startup after a turnaround
  • Significant operation or process changes.
  • Start-up after major maintenance.

Purpose of PSSR

Basically, the primary purpose of PSSRs is to avoid workplace incidents and resultant damage to assets and mankind. The main purposes behind the pre-startup safety review can be listed as follows:

  • PSSR ensures that installations conform to the original design and operating intent of the plant.
  • It confirms that safety, operating, maintenance, and emergency procedures are taken care of and adequate.
  • The pre-startup review ensures that all safety workshops like HAZOP study, model review, HAZID, etc are completed during the detailed engineering phase.
  • It also ensures all site modifications during the construction phase are recorded and controlled.
  • PSSR emphasizes that employees involved in the operating process are properly trained.

A pre-startup safety review is also sometimes known as a pre-startup safety audit (PSSA) and it gives the plant owners the authority to refuse the plant responsibility when PSSR is not performed.

The Pre-Startup Review Team

The PSSR team will be a multi-disciplinary team consisting of various disciplines. The Head of Operations (or sometimes Lead Project Engineer) is generally the leader of the PSSR team. Depending on the type of project, the following professionals are usually included in the PSSR team:

  • A knowledgeable and authoritative supervisor
  • Design and construction personnel
  • Engineering personnel responsible for the design of the project.
  • Instrument and controls personnel
  • Maintenance personnel or their representative.
  • Operations personnel or their representatives.
  • Safety personnel
  • Environmental specialist.
  • Emergency response department representative.
  • Inspection department representative.
  • Industrial hygiene representative.

The team should a minimum of three people to a maximum of 10 people. One person from the team can perform multiple roles.

Key Steps involved in a Pre-startup Safety Review

The important steps in a PSSR must be written in a PSSR procedure. Some of the important steps are:

  • PSSR team meeting to explain the PSSR purpose and decide on the PSSR checklist. Reviewing P&ID and all other relevant documents.
  • Visit the actual site and control room to find out about start-up readiness.
  • Review all items physically following the exhaustive checklist and noting down action points if any.
  • Working on the action points by the relevant discipline and tracking and once satisfied team sign-off.
  • Proper documentation of all the actions performed.

PSSR Checklist

The PSSR checklist is an important document that lists all the required actions to be reviewed while the pre-startup safety review process. The PSSR checklist must include all the key elements that impact any process safety information change. A typical PSSR checklist can be found here.

References and Further Studies

To learn more about the PSSR process and its importance, the following documents can be studied:

What is an Orifice Flowmeter? Its Working, Installation, Types, Advantages, and Disadvantages

Written by Anup Kumar Dey in Instrumentation

The orifice flow meter is a device widely used for flow measurement applications in the Oil & gas industry. The orifice flow meter is capable to measure the flow rate of both services (Liquid & Gas) and steam service. An orifice plate is used to create the differential pressure in the process line by acting as an obstruction for flow. The flow rate passing through the orifice in the processing pipeline is directly proportional to the square root of differential pressure (Pressure Drop).

The orifice plate is fitted into line with the flanged connection in the pipe of the process line. The orifice bore diameter size is smaller than the pipe diameter, thus reducing the area which means a lower flow rate is passing through the orifice construction. The location at which the orifice meter cross-sectional area is minimum and fluid tends to regain energy after this point is called the Vena contracta. 

Principle of Orifice Flowmeter

The principle on which the orifice meter works is the differential principle. Flow rate is calculated when fluid (Liquid or gas) is passed through the Orifice flow meter, differential pressure is generated.

According to Bernoulli’s equation, the flow rate is directly proportional to the square of the pressure drop. The flow rate is calculated from the differential pressure indicated on the display of the orifice flow meter.

“Reduction in flow passage accelerates the fluid thus pressure difference is created. Measurement of flow rate is based on the inlet pressure and pressure reduction point to give a discharge flow rate of pipe”.

Important technical terms in Orifice Flowmeter

Some key terms are important terms for the understanding of orifice meter design and working principle.

Beta ratio (β):

The beta ratio is the ratio between the diameter of the orifice bore to the inside diameter of the pipe.

Beta (β) = Orifice Bore Diameter (d) / Internal Pipe Diameter (D)

The beta ratio has no standard range, recommended range for the beta ratio is between 0.2 – 0.7.

Case if the beta ratio is less than 0.2 (Beta ratio < 0.2):

In this case, the following observations are found:

  1. The diameter of the orifice bore is small.
  2. High-pressure drop, hence higher flow restriction.
  3. Increase in uncertainty and decrease in accuracy.
  4. Chances of cavitation and flashing take place, because higher pressure drop line pressure may go below the vapor pressure of the fluid.

Case if the beta ratio is greater than 0.7 (Beta ratio > 0.7):

In this case, following observations are found:

  1. The diameter of the orifice bore is larger.
  2. Low-Pressure drop, hence minimum the flow restriction.
  3. Experiences difficulty in measuring low-pressure applications service.

Reynolds Number:

Reynolds number plays an important role in the selection of the type of orifice plate. Reynolds number is the ratio of inertial forces to viscous forces. 

At low Reynolds number flow geometry or profile gets disturbed, a Reynolds number greater than 10000 is recommended so that the coefficient of discharge becomes constant throughout the indicated curve below.

Selection of differential pressure transmitter range:

At full flow conditions differential pressure range between 0 to 2500 mm H2O (0 – 25 KPA or 0 – 100 inch of water) is adopted very commonly for the orifices.

Refer below-shown figure shows that the 0 – 100 Inches DP range is sufficient in which curve minimum error, due to the change in density to the change in temperature. This range of differential pressure also indicates that accuracy is maximum than the other cases.

Installation of Orifice flow meter:

Orifice-type flow is directly installed in the process line using the flanged connection. The orifice meter consists of taps for pressure measurement which are connected to a pressure measuring device situated according to the design construction. 

Precautions during installation

Within a 1 or 1.5-meter distance, there is no requirement of fitting a nearby Orifice flow meter. The upstream and downstream run is required for the orifice flow meter for velocity distribution.

How does an orifice flow meter work?

Orifice flow meter installed with known coefficient of discharge. Air pocket removal from tubing is necessary before the operation of the flow meter. The orifice flow meter assembly consists of an orifice plate which creates the pressure drop. Process fluid is flowing through the line, and passed through the orifice meter construction. The velocity of process fluid in the pipeline is irregular during initial operation, in a later stage fluid velocity gets stable, and the created pressure drop is measured by the pressure gauge on the taps. 

Thus pressure drop is used to calculate the volumetric flow of the stream indicated in the display of the orifice meter. Fluid density is multiplied by the volumetric flow to calculate the mass flow rate of the Process fluid.

Types of Orifice Plates in Orifice Flowmeter

Orifice flow meters consist of mainly four types of orifice plates which are described below:

Types of Orifice Plates
Fig. 1: Types of Orifice Plates

Eccentric orifice plate

Eccentric type orifice plate in which borehole is typically constructed off center, square edged. This type of construction is helpful to prevent the deposition of solid and other unwanted materials present in process fluid on the surface which can block the orifice bore. 

The eccentric orifice plate is capable of calculating the flow rate of fluid-carrying gas within the liquid phase (Mixture Phase). The degree of uncertainty is far greater in the Eccentric type in comparison with the concentric type orifice plate.

Concentric orifice plate

A concentric orifice with a center bore design is most commonly used in the application. The concentric orifice plate is a proven and reliable technology that is adopted at the global level. Manufacturing of concentric is also simply by machining a thin plate to create a circular hole in the middle portion of the plate. Concentric orifice plate consisting of a square edge.

Segmental Orifice Plate

In this type of orifice, the plate borehole is centered and consists semicircle shape, with a square edge. Segmental orifice plates are designed for a low amount of slurry and a high amount of solid concentration in the fluid. This type of orifice is an expensive and higher degree of uncertainty in comparison to an eccentric orifice plate.

Quadrant radius orifice plate

This type of orifice plate is designed like a nozzle in which upstream construction is lesser sharp in comparison to the downstream design construction. They are designed for flow containing Reynolds numbers less than 10000 and viscous media properties.

Advantages of Orifice flow meter

  • Simple in construction 
  • Low space requirement
  • Relatively cheaper

Disadvantages of Orifice flow meter

  • Poor pressure recovery
  • Not suitable for low-pressure application
  • Higher power loss

Click here to learn about types of flowmeters and their applications

What is Level Measurement? Its Types, Working, & Advantages

Written by Anup Kumar Dey in Instrumentation

Level measurement is a process of measuring/monitoring the fluid level within equipment (i.e. Vessel, Reactor, and Storage Tanks). Level measurement may be a Point level or continuous type which can be achieved with the help of a sensing element called the sensor.

Objectives of Level Measurement

There are several technologies available in the instrumentation Industry, Level Measurement is an essential activity in process engineering. The main objectives of level measurement are below mentioned with the possibility of Zero error. 

  1. Online level measurement means a digital display of output data for alarm, trip, and record data as well.
  2. Increases process Efficiency
  3. Tackle or avoid Safety Related incidents

Types of Level Measurement

Level measurement techniques are mainly classified into two categories which are the following:

  1. Point Level measurement
  2. Continuous Level measurement

These two classifications of level measurement sensors are briefly described below:

Point Level Measurement:

Point level Measurement referred to as the instrument will produce the output or measure value when the level reaches a certain level (up to or greater than the Sensing element of the Level Instruments) within the equipment. Selected media (fluid type) used for level may be liquid, solid, or slurry.

Examples of Point level measurement sensors: Capacitance, Conductivity, Tuning fork

Level Indication basis in Point level measurement: This type of measurement detects high/low-level points where high is set to keep the equipment safe from future overfilling incidents & low to keep the plant safe from downtime.

Types of Point level measurement techniques:

Working of capacitance type sensor:

Capacitance-type sensors are rod-shaped like level measurement which is inserted from the top of the equipment. This type of level sensor works over the principle of change in capacitance.

Capacitance is directly dependent upon the amount of Fluid present within the Equipment. The thermal capacitance of process fluid gradually increases as the level inside the equipment increases and vice versa. Installation of this type of sensor is usually top-mounted.

Advantages of Capacitance type sensor: 

  1. Suitable for liquid & solids.
  2. Cost-effective solution
  3. Used for Viscous media
  4. No mechanical or moving parts
  5. Small in construction
Types of Point Level Measurement Techniques
Fig. 1: Types of Point-Level Measurement Techniques

Working of Conductivity type sensor:

This type of sensor is also rod-shaped consisting of a pair of electrodes with the probe. An alternating current from an external source is supplied to the sensor. When the fluid level inside the equipment reaches up to the sensor, supplied alternating current helps to complete the circuit which causes current to flow. Thus fluid levels are calibrated from the output current value. Installation of this type of probe switch is usually top-mounted.

Advantages of Conductivity type sensor:

  1. Available at low cost
  2. Easy to use
  3. No mechanical or moving parts

Working of Optical type level sensor:

Working of optical type level sensors based on the emission of infrared light towards the application media. The principle used by the optical type level sensor is total internal reflection.  

IR Light is emitted from the LED source called the sender, and the source which collects back IR light is called the receiver this all activity takes place within a prism arrangement. As emitted IR light from the sender gets absorbed or reflected in the application media, thus remained IR light is sent back to the receiver. Reflection of the IR light helps to detect the present liquid level.

Advantages of Optical type level sensor:

  1. Compact Size
  2. No Moving
  3. Inexpensive & Effective Solution

Working of Tuning fork type sensor:

Tuning forks have been used in level measurement since the 1970s. The working principle of the fork sensor is dependent on the application media which completely uses vibrations.

Case-I (Applicable for solid Media): The amplitude of the Vibration principle is used in the case of solids where a fork continuously vibrating at constant intervals gives an amplitude value let’s say X, this amplitude value acts as the threshold value.

When the solid material present inside the equipment contacts with the vibrating fork, the oscillation of amplitude gets changed from X. When this amplitude value goes below X which is the threshold value with the help of an inbuilt electronics system causes changes in output (Calibration or calculation of media level). 

Vibrating Fork Level Sensor for Solids
Fig. 2: Vibrating Fork Level Sensor for Solids

Case-II (applicable for liquid media): The principle is used “Frequency of operation” the in which frequency threshold value is generated due to the vibration of the tuning fork.

The natural Frequency of the fork gets reduces when the liquid media increases inside the equipment. Level measurement is calibrated in the condition when the natural frequency matches the threshold frequency.

Vibrating Fork Level Sensor: Factory Calibration
Fig. 3: Vibrating Fork Level Sensor: Factory Calibration

Advantages of tuning fork type level sensor:

  1. Compatible with high-temperature fluid
  2. Not affected by the flow behavior (i.e. turbulence, foaming, etc.)
  3. Small in size & easy to installation

Continuous Level Measurement:

Continuous Level measurement refers to the measurement in which media is present in the equipment from the ground level to the peak (top) Level. Continuous Level measurement can be used for liquid or solids.

Level Indication basis in Continuous Level monitoring: In this type of level measurement, each output value changes as fluid rises or down. The set Point can be decided from the range measured.

Types of continuous-level measurement techniques: 

Working of Ultrasonic level sensor:

Ultrasonic type level sensor working principle based on the ultrasonic waves. Ultrasonic waves are emitted by the head of the sensor which is passed through the fluid media and finally gets received by the receptor of the sensing element after striking the bottom surface of the equipment. The time difference between ultrasonic wave emission & reception is used to calculate the distance (i.e. level). Ultrasonic waves used are sound waves for level measurement.

The level can be calculated by the equation:

Distance L = 1/2 × T × C

Where, 

  • T is the time difference between the emission & reception of waves (1/2 is used in the equation for wave travel for both emission & reception path).
  • C is sonic speed 
  • L is distance 

Advantages of Ultrasonic level sensor:

  1. The sensing element does not come in direct contact with application media
  2. Low cost-effective solution
  3. Not affected by the environmental condition (moisture, high ambient temperature)

Working of Radar type level sensor:

The radar-type level sensor working principle remains the same as in the ultrasonic-type level sensor case. Radio waves are responsible for level measurement instead of sound waves used in the ultrasonic-type level sensor. Radio waves are released from the antenna which is placed at the top of the equipment after striking the bottom surface these returned signals are received by the antenna as well. 

Level measurement is achieved by the time difference between emission & received signals.

Advantages of Radar type level sensor:

  1. Non-contact type with application media
  2. Gives high-accuracy measurements.
  3. Suitable for vacuum & high-pressure applications.

Working of DP Type level sensor:

This type of level sensor work on the pressure difference. Two sensors are placed at low-pressure & High-pressure regions. The level is measured from the equation

Pressure = Density of fluid * acceleration due to gravity * Height 

Rearranging equation;

Height = Pressure / (Density of fluid * acceleration due to gravity)

The density of process fluid remains constant for an accurate result.

Advantages of DP Type level sensor: 

  1. Easy to install & removal
  2. High accuracy
  3. Easy maintenance & testing (block valves provided to keep instrument isolated from process fluid).

Causes / Impacts of Incorrect Level Measurements

  • Case – I: If the measured level is lower than the actual level. It may produce an impact on the equipment (may damage).
  • Case – II: If the measured level is High than the Actual level. Safety (instruments with their alarm, trip interlocks) & environmental Norms or standards are halted.

Piping Specialty Items and Their Review

Written by Saurabh Shetty in Engineering Materials

Piping Specialty items are basically a range of non-fitting items and components required to serve various functions in the piping and plumbing system. The scope of this article is to take you through a brief introduction to the Piping specialty items and their review.

When an item cannot be managed as a bulk item due to certain Process Licensor requirements, it must be procured as a special item (as these special parameters need to be informed to the vendor which cannot be done through bulk purchasing.) The first step towards this direction is marking it with a special tag on PID for easier identification on site. These special items are depicted with a symbol on the PID. Hence the process of assigning the Special item tag is important and there should be no duplication. These special items usually have a longer lead time as compared to bulk items and being special, they are also expensive.

It is also important to have the correct data as per the P&ID so that the sizes, ratings, or materials are not wrongly purchased.

Once the special tags are assigned and the list is prepared, the purchase specification is then prepared for each special item, including the scope, the material, design, end connection, packing, preservation, and painting requirements as such. The process datasheets involving the different process inputs for the individual special item are further attached to this purchase specification.

The Material requisition (which consists of the purchase specification, the process datasheets, the painting, preservation, inspection, and test plan) is then floated in the market for vendor offers. After receiving the vendor offers, the technical bid evaluation is done (which involves to and fro technical queries, which are resolved between the contractor and the vendor). Once the technical bid evaluation is finalized, it is then forwarded to the Procurement department after which the purchase order is finally placed. Then we receive the general arrangement drawings for each special item which needs to be reviewed and further approved across subsequent revisions. After which they are ready for production and further dispatched to the site once ready.

Some of the special items involved are steam traps, strainers, angle piston valves, flame arrestors, special check valves, flexible hoses and quick couplings, and sight glass.

We will just go through a quick and brief introduction for every special item mentioned above.

Steam Traps

During the heat transfer process for example in a heat exchanger, both air and condensate can form and get trapped in the system, making it less effective. Hence steam traps are basically used to separate out these condensate and non-condensate gases (like air) from a pressurized steam system. Therefore, steam traps are used to trap steam and discharge the condensate. The heating efficiency in the system would be affected if the condensate is not removed, and quickly.

There are different parameters such as pressure drop, sizing, condensate load, density, flow rate, viscosity, design pressure, temperature, etc. to be considered in a trap datasheet.

There are many types of steam traps used depending on the application such as

  • Thermodynamic steam trap (works on the principle of pressure differential).
  • Thermotactic steam trap (works on the principle of temperature differential).
  • Mechanical traps such as ball float type and inverted bucket type.

The vendor or the process engineering department shall select the right type of trap depending on the application, the differential pressure, and the condensate and sizing load.

Most of these steam traps are equipped with integral strainers for filtering purposes.

Generally, from the above, thermodynamic traps are widely used. They are also used as utility traps commonly referred to as bulk traps. They are cheaper as compared to other traps. To know more about steam traps click here. Below are the pictures of the steam traps.

Types of Steam Traps
Fig. 1: Types of Steam Traps

Strainers

The strainers are used in process plants to protect equipment such as valves, and steam traps from dirt, etc. The mesh size, pressure drop, opening area ratio, design temperature, and pressure are different parameters to be considered in the datasheet for strainers.

The different types of strainers are Y-type strainers, T-type strainers, Basket type strainers, and Conical type Temporary strainers.  Below are the pictures of the strainers as mentioned above. More details of strainers can be found here.

Types of Strainers
Fig. 2: Types of Strainers

Angle Piston Valves

These are one of the most critical piping specialty items, they are mostly used at the bottom of equipment such as reactors. They have a long lead time and are also expensive.

The alpha angle of the drain connection with respect to the flow, the special service and finishing requirements, design temperature and pressure, and layout considerations, if any shall be taken into account whilst preparing the datasheet for angle piston valves.

Flame Arrestors

While transporting flammable liquids or gases, there is a possibility of flame or explosion to occur should an ignition take place.

The explosion group, the type of service, the zone classification, design pressure, temperature, and layout considerations shall be considered whilst preparing the datasheet. The vendor shall select the type of flame arrestor depending on the above parameters. There are two types of flame arrestors:

Detonation:

Inline detonation flame arrestors are specifically designed for pipelines that have a significant distance between the ignition source and the flame arrestor. In other words, they can be installed at any distance from the ignition source. They offer ultimate protection from a worst-case scenario i.e of an explosion. They have a series of mesh as shown in the figure below and based on all the above reasons they are expensive when compared to the deflagration type.

Deflagration:

End-of-line deflagration is designed to protect against atmospheric deflagration where the ignition source originates outside the system.

Inline deflagration is designed to prevent the possibility of propagation of flames in the piping systems by locating the flame arrestor in close proximity to the potential source of ignition.

Various Types of Piping Specialty Items
Fig. 3: Various Types of Piping Specialty Items

Special Check Valves

Special check valves are similar to normal check valves except that they would have some special process requirements individually such as pressure drop, density, design temperature, and pressure, etc. which cannot be managed through bulk and would require a different special item tag. These special process parameters shall be taken into consideration whilst preparing the datasheet.

Flexible Hoses and Quick couplings

Flexible hoses along with quick couplings are used for process and utility services (Plant air, Cooling water, Nitrogen, and Steam). The end connections, the design pressure, and temperature, the length of the hose required are certain parameters that require to be included in the datasheet.

Different ends connection for the hose such as Camlock type, wing nut type, and Swagelok type are used depending upon the services.

Sight Glass

Sight glasses as piping specialty items are pieces of equipment with industrial glass used to observe the levels of liquids in a plant. They allow the plant personnel to monitor the pressure changes. The different process parameters here are given by process. The design conditions such as pressure and temperature, fluid service, and the type of glass required are certain parameters to be included in the datasheet.

List of Piping Specialty Items

Some of the most common piping specialty items are already introduced in the above section. Some other piping specialty items are listed below:

  • Static Mixer
  • Special Equal Tee
  • Grit trap
  • Sand Trap
  • Liquid Trap
  • Air release vacuum breaker
  • Bug Screen
  • Chemical Injection
  • Insulation Joints, Insulation Flanges, Insulation Kits
  • Bursting Discs
  • Sample cooler
  • Valve interlock
  • Quick release Coupling
  • Oblique Connection
  • Corrosion Coupon
  • Pipe Expansion Joint
  • Corrosion probe
  • Fabricated and Special forged items and nozzles according to customer drawings
  • Test Plugs
  • Ball Joints
  • Flexible Connectors
  • Fire Hydrant

Types of Heat Exchangers and Their Selection

Written by Anup Kumar Dey in Process

A Heat Exchanger is a mechanical device that is used to exchange heat between fluids. The fluid used for heat transfer operation can be in the gas or liquid phase as per the availability. The number of fluids used for heat transfer operation maybe two or more. A properly designed heat exchanger can be used for both heating & cooling operations.

Heat exchangers are widely used in chemical plants, refrigeration and air conditioning systems, petrochemical facilities, food and beverage industries, and nuclear and power industries. As the heat exchanger does not have any rotating component, they are known as static equipment. Most of the heat exchangers are designed based on ASME BPVC Sec VIII codes or TEMA guidelines.

Heat exchangers are usually manufactured from materials that are heat-resistant. Some of the most common heat exchanger materials are Carbon Steel, Stainless Steel, Alloy Steel, Aluminum, Copper, Titanium, DSS, Hastelloy, Ceramics, Composite Plastics, etc. In this article, we’ll learn about the Classification of Heat Exchangers.

Classification of Heat Exchangers

Classification of Heat exchangers is dependent on several factors such as

  • Flow configuration,
  • Pass configuration
  • Heat transfer mechanism,
  • Construction method,
  • Function and application,
  • Fluid phases, etc.

A. Heat Exchanger Types based on the Flow Configuration

Flow configuration simply refers to the arrangement (path) provided within the heat exchanger. This is an indication of the fluid traveling direction of the heat exchanger. Flow configuration in heat exchangers consists of the following four types:

  1. Co-Current Flow
  2. Counter Current Flow
  3. Cross Flow, and
  4. Hybrid Flow

Co-Current Flow Heat Exchangers:

Co-Current flow Heat exchangers are also known as parallel flow heat exchangers. In this type of heat exchanger, the flow of fluid streams is parallel to each other and the operating fluids are moving in the same direction. Co-Current flow heat exchangers provide thermal uniformity across heat exchanger walls and usually have lower efficiency.

Counter Current Flow Heat Exchangers:

The heat exchangers where the direction of the fluid is parallel but opposite (divergent) to the other are known as counter-current type heat exchangers. They usually have the highest heat exchange and greatest temperature change.

Types of Heat Exchangers based on Flow Configurations
Types of Heat Exchangers based on Flow Configurations

Cross Flow Heat Exchangers:

When the flow of the fluids inside the heat exchanger is perpendicular (formation of right angle ~ 90° while flowing) to each other, they are called cross-flow heat exchangers. In terms of efficiency, a cross-flow heat exchanger gives better efficiency than the parallel flow configuration type heat exchanger.

Hybrid Flow Type Heat Exchanger:

Hybrid flow configuration uses a combination of the above-mentioned flow configurations, i.e. Co-Current, Countercurrent, or Cross Flow any of the mentioned combinations may be used within the single process. To accommodate the limitations of a single type of heat exchanger, this type of heat exchanger is produced.

B. Types of Heat Exchangers based on the heat transfer mechanism

According to the heat transfer process, heat exchangers are classified into direct contact type heat exchangers & indirect contact type exchangers.

Direct contact type heat exchanger:

This type of heat exchanger does not contain a wall tube for different fluids for the heat transfer process. The fluids come into direct contact to exchange heat between each other & exit via their respective outlet nozzles or line. Due to direct heat exchange, very close temperatures can be attained. Examples: Direct contact type process utilizes by the cooling tower, desuperheater, and Scrubber.

Indirect contact type heat exchangers:

This type involves the heat exchange between hot & cold fluid across a construction wall (The separating wall used is generally a tube/ pipe/vessel). As the wall separates the fluid, they do not mix during the whole heat transfer process.

Indirect contact type heat exchangers are further classified into

  • Direct transfer type,
  • Storage Type, and
  • Fluidized Bed type.

Direct Transfer Type heat exchangers: This type of heat exchanger consist of a separate path for each fluid including their respective passes. The heat transfer is based on the temperature gradient (difference). Direct transfer type heat exchangers are also known as recuperators. Continuous heat exchange occurs from the hot fluid to the cold fluid.

Examples of direct transfer type heat exchangers are Shell & Tube heat Exchangers (STHE), Plate type heat exchangers, tubular heat exchangers, and economizers used in power engineering.

Storage Type heat exchangers: This type of heat exchanger is provided with a fixed bed area across which fluid is about to pass through each bed. Hot & cold fluid passed through their beds respectively & valves at the inlet, the outlet is adjusted so that hot fluid is passed through the cooled fluid bed, same is applicable for the cold fluid which is passed through the hot fluid bed, and hence heat transfer takes place through this mechanism.

Example of Storage Type: An air preheater is a suitable example for this type of heat exchanger, ambient air taken into APH & hot fluid heated from the heater emit flue gases which need to be taken out through a stack, flue gas at high temperatures emissions give lower efficiency to the heater so the temperature of flue gas to be lowered by the ambient air whose temperature is increased at the APH Outlet, hence flue gas temperature decreases as both flue gas & ambient air simultaneously passed through each other.

Indirect Contact Type Heat Exchangers
Indirect Contact Type Heat Exchangers

Fluidized Bed type: Fluidized bed type heat exchangers consist of two-compartment; one for hot fluid & cold air for the inlet distributor plate is placed in each section (i.e. hot gas, cold air). The bed is completely filled with alumina pallets. The hot gas causes the alumina to fall into the lower chamber which is primarily used to heat the cold air. It gets heated up from hot gas which is flowing in the upper chamber. A recirculation path or arrangement is incorporated for recycling purposes.

In the Fluidized bed heat exchanger, solid particles or pallets are placed at the bottom, at low operating fluid velocity fluid is passed through the pallet bed, high velocity causes the solid particles to float in the entire section volume as drag force of fluid is greater than the weight of fluid.

C. Heat Exchanger Types based on the pass configuration:

Depending on the pass configuration used in the heat exchangers they can be grouped into any one of the following types:

Single-pass heat exchanger: In this type of heat exchanger, the fluid can pass once through the length of the heat exchanger.

Multi-pass heat exchanger: This type of passing arrangement utilizes the U bends and the fluid moves through the heat exchanger length more than once. The design of a multipass heat exchanger involves a series of tubes.

D. Types of Heat Exchangers based on the available Fluid phases:

Depending on the fluid media phases involved in the heat transfer process, three types of heat exchangers are found. They are

  1. Gas – Liquid: This type involves the application in the compressor oil cooling arrangement is required.
  2. Liquid – Liquid: This type of Heat Exchanger is used very commonly in the process industry. Shell & tube heat exchanger is a common example.
  3. Gas – Gas: This type of heat exchanger is used in a process where air pre-heating is required which is through APH (Air pre-heating).

E. Heat Exchanger Classification based on Functions and Usage

Depending on the process function and application, there are various types of heat exchangers as listed below:

  • Exchangers
  • Coolers
  • Condensers
  • Chillers
  • Reboilers
  • Non-fired Heaters
  • Evaporators
  • Steam generators

F. Classification of Heat Exchangers based on Construction

Depending on the construction features, heat exchangers can be classified into different types as follows:

  • Shell and tube heat exchangers
  • Plate-type heat exchangers
  • Air-cooled heat exchangers
  • Spiral heat exchangers
  • Finned tube heat exchangers
  • Double-pipe heat exchangers

Selection of Heat Exchangers

Selecting the proper type of heat exchanger from such different options available is a difficult task. The selection of a specific type of heat exchanger is usually done by the process engineer during the design phase. Many parameters must be considered while selecting the right heat exchangers. Some of these factors that impact the heat exchanger selection process are:

  • The type of fluids, the fluid stream, and their properties (Fouling characteristics of the fluids)
  • The desired thermal outputs (Temperature driving force)
  • Size limitations (Plot plan & layout constraints)
  • Application
  • Design and Operating pressures & temperatures
  • Available Utilities
  • Costs
    • purchase cost
    • installation cost
    • operating cost
    • maintenance cost

In general, more than 50% of all heat exchangers installed are Shell-and-tube heat exchangers. The following image provides a rough idea of how the heat exchanger selection varies with design temperature and pressure.

Selection of Heat Exchangers
Selection of Heat Exchangers with respect to Design temperature and Pressure