Adjusting Temperature Control: A Look at Heat Exchangers in Piping

II JAY SHRI KRISHNA II

Heat exchanging is a necessary part of Piping systems. It confirms precise temperature control, enhances efficiency and cost savings, improves system performance and adds to environmental benefits. Without efficient heat exchange, maintaining proper temperatures in Piping arrangements would be difficult & potentially lead to a range of problems.

Let’s understand briefly about Heat Exchanger, its function, working principle, their types, application, limitations and lots more…!!

Adjusting Temperature Control: A Look at Heat Exchangers in Piping

Heat Exchanger is a very significant equipment used in many process plant for different purposes like heating, cooling, boiling or phase change etc.

Shell and Tube Heat Exchangers in Piping

What is Heat Exchanger?

It is an equipment that transfers thermal energy i.e. Heat transfer occurs between two or more fluids at dissimilar temperatures. They are basically controlled heat transfer machines, allowing the heating or cooling of fluids without them directly mixing.

Function of a Heat Exchanger in Piping:

In Piping systems, Heat Exchangers work for the primary function of regulating fluid temperatures. They can be used for:

Heating: Transferring heat from a hot fluid to a cold fluid which, results raising the temperature of the cooler fluid.

Cooling: Transferring heat from a hot fluid to a cold fluid which, results lowering the temperature of the hot fluid.

Working Principle of a Heat Exchanger:

Heat Exchangers functioning is created on the principle of conduction. The hot & cold fluids run through separate channels within the exchanger which are separated by a solid wall. This wall conducts heat from the hotter fluid to the colder fluid. The rate of heat transfer is influenced by the wall's surface area, the materials it's made of, and the flow rates of the fluids involved.

Heat Transfer occurs in three main ways:

Conduction: Direct collision of tiny particles in a solid material, passing heat from hot to cold.

Convection: Movement of fluids (liquids or gases) carrying heat along with them.

Radiation: Transfer of heat through electromagnetic waves, like feeling sunshine.

Flow Arrangements in Heat Exchangers:

Parallel Flow (Side-by-Side): Simple design, but low efficiency. Fluids flow co-currently, meaning they enter on the same side and exit together. Temperature difference reduces along the flow path.

Counterflow (Opposite Directions): Most efficient arrangement. Fluids flow counter-currently, entering from opposite ends. This maintains a larger temperature difference throughout for maximum heat transfer.

Crossflow (Crossing Paths): Useful for gas-liquid applications. One fluid flows perpendicularly (across) to the other. Offers a balance between efficiency and pressure drop in the flowing streams.

Hybrid Arrangement: Combines elements of different flow patterns. Imagine a heat exchanger with one section in counterflow for high efficiency and another in crossflow for fluids with pressure drop concerns. This permits for optimization based on specific application needs.

Common Parts of Heat Exchanger:

Heat Exchangers come in various designs, but a common type, the Shell and Tube Heat Exchanger, has several key parts:

1. Shell: A cylindrical Pressure Vessel that firms the tube bundle. It's usually made from carbon steel or stainless steel and directs the flow of one fluid either hot or cold around the tubes.

2. Tubes: These are the networks through which the other fluid flows. They are normally made of copper, brass or stainless steel, depending on the request's pressure, temperature and corrosion resistance requirements.

3. Baffles: These are stationary plates placed within the shell to direct the flow of the shell-side fluid across the tubes for better heat transfer. For Baffle construction, carbon steel or stainless steel are the typical material choices.

4. Headers: These are compartments at each end of the tube bundle, that distribute the fluid evenly through the tubes. They are connected with Piping system by nozzles.

5. Nozzles: In a Heat Exchanger, Nozzles act as the entry and exit points for fluids, allowing them to flow in and out of the shell. They are sized as per the flow rate of the fluids.

6. Tube Sheet: A plate at each end of the shell that holds the tubes in place. The tubes are place closed to the tube sheet to prevent leakage between the two fluids.

Some Heat Exchangers may have additional parts depending on the specific design & application. These can include:

Expansion Joints: These are flexible bellows that absorb thermal expansion & contraction of the components to prevent stress and leaks.

Supports: Heat Exchangers requires structural supports to withstand their own weight as well as weight of the fluids they contain.

Insulation: This is applied to the shell to minimize heat loss to the surroundings or heat gain from the environment, depending on the preferred process.

Types of Heat Exchangers in Piping Systems:

There are several types of Heat Exchangers used in Piping systems, each with its specific advantages & applications. Here are some common types:

Shell and Tube Heat Exchanger: It consists of a shell which, enclosing a bundle of tubes, which features two fluids: one travels through internal tubes, while the other flows around them within a surrounding shell.

Plate Heat Exchanger: This type of exchanger uses thin, corrugated metal plates to create a large surface area for heat transfer. They are compact & capable for transferring heat between fluids with similar pressures.

Air-Cooled Heat Exchanger: This type of exchanger uses air as the cooling fluid. It involves of a finned heat transfer, surface through which hot fluid flows and air is blown over the fins to remove heat.

Water-Cooled Heat Exchanger: This type of exchanger uses water as the cooling fluid. It is similar to the Shell and Tube Exchanger but, uses water instead of air on the shell side.

We will understand all types of various exchangers briefly in coming next blogs exchanger series… so stay tuned with us…!!

By understanding the role & different types of Heat Exchangers in Piping systems, we gain appreciation for their critical role in regulating temperatures within various industrial processes.

Here are some key points to remember while routing piping for a Heat Exchanger:

General Guide Lines:

Provide shell with pressure relieving element to protect against extreme shell side pressure in the event or internal pressure.

Place corrosive fluids inside the tubes as these are simply cleaned & cheaper to replace than the shell.

Put hot fluid in the tubes of exchanger to reduce heat loss to the surrounding.

If steam is use to heat the fluid in the exchanger so that passing the steam through the shell has advantages. As condensate is easy to handle as well as simplifies condensate management from the shell side.

Insulation on shell is normally required to protect person safety, to reduce the rate of condensate formation and to reduce heat losses.

For economic operation, carrying cooling liquid through the tubes if the exchanger, if not insulated.

If the heat transfer is between two liquids, then a counter current flow pattern will usually provide to give greater overall heat transfer than a parallel flow pattern.

Arrange all nozzles to suit best piping routing & plant layout.

Locating Heat Exchanger:

Practically, Heat Exchanger is placed perpendicular to pipe rack. Locate exchanger at right place so that piping is as direct and simple as possible. Lift up Heat Exchanger to allow piping to the exchangers bottom nozzles to be set above grade or floor level.

Space and Accessibility:

Functioning space for davit, monorails or crane etc.

Space is compulsory given for tube bundle removal for cleaning & around the exchangers bolted ends & the bolted channels to shell enclosure.

Providing access for tube bundle removal is often given on manufactures drawings & is usually about 1.5 times the bundle length. 15 to 20ft clearance should be allocated from the outer side of exchanger in order to mobile lifting equipment access & easy tube handling.

Operating and maintenance Requirement:

Exchangers are sometimes of need mounted on structures, process column & other equipment then special arrangements are provided for maintenances & tube handling to be required.

Consider insulation thickness: Account for the added thickness of insulation on the exchanger and piping when determining clearances.

Provide access for operating valves and instruments: Ensure easy operation and visibility of valves, pressure gauges, level indicators, etc.

Maintain headroom: Keep piping elevated a safe distance from platforms to avoid obstructing movement or causing head injuries.

Allow for maintenance: Ensure enough clearance around the exchanger for removing channel heads, covers, or the entire unit if necessary.

Stress and Flexibility:

Minimize thermal strain on nozzles: Route piping to avoid pushing excessive stress on the exchanger's nozzles due to pipe weight, thermal expansion or contraction.

Incorporate flexibility: Use expansion joints or bellows to provide somewhere to stay thermal movements & prevent pipe strain.

General Considerations:

Minimize piping length and fittings: Aim for the shortest possible route with the least number of elbows, tees, etc. This reduces cost, pressure drop & potential leak points.

Avoid traps and pockets: Remove sections where fluid can collect and stagnate, as this can lead to corrosion or hinder drainage.

Attempt for one high and one low point: This simplifies venting and draining of the Piping system.

Additional Considerations:

Piping layout vs. equipment arrangement: Consider positioning exchangers strategically e.g. side-by-side or stacked to adjust piping runs.

Compatibility with piping code: Confirm your routing adheres to relevant piping codes and standards like ASME B31.3 for pressure piping.

By following these guidelines, you can design a piping layout for Heat Exchanger that is well-organized, maintainable and safe.

Heat exchanging is vital in Piping systems for several reasons:

Precise Temperature Control:

Maintaining Process Conditions: Many industrial processes have need of specific temperature ranges for fluids to function correctly. Heat Exchangers confirm these temperatures are achieved & maintained, preventing failures or product spoilage.

Safety Measures: In some cases, too hot or cold fluids can pose safety hazards. Heat Exchangers help regulate temperatures to avoid overheating or freezing, which could damage or harm equipment or lead to accidents.

Optimizing Efficiency and Cost Savings:

Energy Recovery: Heat Exchangers can capture waste heat from a hot fluid & transfer it to a cold fluid that requires heating. This reduces the total energy consumption of a system, lowering operational costs.

Reduced Reliance on External Heating/Cooling: By efficiently transferring heat within the system, Heat Exchangers can reduce the need for additional heating or cooling equipment, leading to cost savings on both equipment & energy usages.

Improved System Performance:

Preventing Equipment Damage: Uncontrolled temperatures can damage pipes, valves and other components in a Piping system. Heat Exchangers help to prevent such damage by regulating temperatures within safe operating ranges.

Enhanced Process Consistency: Constant temperatures contribute to predictable & reliable performance in various industrial processes. Heat Exchangers play a significant role in maintaining this process consistency.

Environmental Benefits:

Reduced Energy Consumption: As said earlier, efficient heat exchange translates to lower energy usage, which can significantly reduce greenhouse gas emissions & contribute to a more sustainable operation.

Process Optimization: By optimizing processes & minimizing waste heat, Heat Exchangers can help to lower the environmental impact of industrial activities.

Heat Exchangers: Materials, Applications, Advantages, Disadvantages, and Limitations

Heat Exchangers facilitate the transfer of thermal energy between fluids, simplifying the process. Here's an analysis of their key features:

Materials:

Metals: Common varieties include carbon steel, stainless steel, brass, copper and nickel alloys. These materials offers good strength, durability, and heat transfer capabilities. Heat exchanger selection hinges on factors like temperature, pressure, corrosion resistance, and cost.

Other materials: For specific applications, materials like graphite, plastics e.g., PVC and even ceramics might be used. These offer advantages like lightweight construction, corrosion resistance to specific chemicals or good insulating properties.

Applications:

Heat exchangers have a wide range of uses across various sectors:

Power generation: Cooling condensers in thermal power plants, preheating boiler feedwater.

HVAC (Heating, Ventilation & Air Conditioning): Air conditioning systems, space heating, domestic hot water production.

Refrigeration: Evaporators, condensers in refrigerators and freezers.

Chemical processing: Distillation, reaction heating/cooling, crystallization.

Automotive industry: Engine cooling systems, oil coolers and transmission coolers.

Food and beverage industry: relies on three key processes to ensure safety and extend shell life: pasteurization, sterilization, and fermentation.

Advantages:

Efficient heat transfer: Allows effective use of thermal energy, reducing waste & optimizing processes.

Temperature control: Precise control of fluid temperatures for various applications.

Compact design: Heat Exchangers can be designed for space-constrained environments.

Versatility: Can handle different types of fluids, flow rates & temperature ranges.

Cost savings: By recovering & reusing heat, they can lead to significant energy cost savings.

Disadvantages:

Potential for leakage & pressure drops: Leaks can occur at connections or due to material failure, and pressure drops happen due to friction within the exchanger.

Maintenance requirements: Regular cleaning and maintenance might be required to prevent fouling and ensure optimal performance.

High initial cost: Especially for certain types like plate heat exchangers with specialized materials.

Limitations:

Fouling and corrosion: Fluids can deposit contaminants or cause corrosion over time, reducing efficiency.

Temperature limitations: Materials have maximum temperature ratings, and extreme temperature differentials can be challenging.

Pressure limitations: Similar to temperature, there are pressure limitations for safe operation.

Mixing limitations: Not all heat exchangers are suitable for mixing fluids, especially those with a high risk of contamination.

Conclusion:

Without efficient heat exchange, keeping proper temperatures in Piping systems would be challenging and potentially lead to a range of problems. By understanding these aspects, you can choose the appropriate Heat Exchanger for your specific application and make sure its optimal performance and lifespan.

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