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Circulation Heaters

Circulation heaters are electric process heaters that heat fluids and gases as they flow over the heating elements of a circulation heater. They are versatile all in one units that are used for heating high temperature gases and hard to heat liquids. The heating elements, terminal connections, mounting mechanism, and vessel are packaged as a single unit for easy installation into an outlet pipe. The versatility of circulation heaters is found in how they are installed, which can be horizontally, vertically, or sloped. Their inlet and outlet piping allow liquids or gases to pass through as they are heated. Circulation heaters are widely used in the oil and gas industry to control the viscosity of oil.

Pressurized or non-pressurized fluids are effectively heated using direct or indirect circulation heaters, which are also known as in-line or re-circulation heaters. The types and varieties of circulation heaters take several forms and include typical standard designs as well as custom designs for special applications. Circulation heaters are engineered with different power ratings, sizes, flow capacities, and can be built to meet the needs of any application.

Types of Circulation Heaters

Circulation heaters are categorized according to their heating mechanism, which can be electrical, steam, or hot oil. In addition, they can be configured to provide direct or indirect heating with direct heating circulation heaters having fluids or gases flowing over heating elements. Indirect circulating heaters heats fluids or gases as they flow through a closed loop system, but do not make direct contact with the heating elements.

Electric

Electric circulation heaters use resistive elements that convert electrical energy into heat using electrical resistance. The generated heat heats the fluids or gases that pass through the heating element. Electric circulation heaters can be direct or indirect with indirect electric circulation heaters using conduction, convection, radiation, or a combination of heating elements.

Steam

Steam circulation heaters are applicable for industries where steam is easily available. Process steam circulation heaters are used in applications that require heating elements that can be finely controlled to a set point. Steam-based circulation heaters provide heat up to 338o F (170o C) and are powered by low-cost fuel. Cogeneration circulation heaters use heat electricity and steam.

Oil

Hot oil circulation heaters are used for applications that have high operating temperatures. With hot oil circulation heaters, oil is pumped in through an inlet. Inside the heater, the oil is heated using electrical resistance. A closed looped system is used to carry the heated oil to a process. Hot oil circulation heaters are an indirect heating method. They are widely used for heating viscous fluids and processes that require high thermal efficiency.

Components of Circulation Heaters

An important consideration when selecting a circulation heater is the materials used in its construction. Each form of circulation heater consists of a tubular flanged immersion heater mounted in a heating chamber that is equipped with a flanged inlet and outlet connection, mounting studs, insulation, and a jacket.

The standard materials used for the construction of circulation heaters are steel, 316 stainless steel, and alloy steels 800 and 804. For specialized applications, metals are treated to withstand chemical compositions and corrosive substances. Direct circulation heaters have inlet and outlet piping that allows liquids and gases to pass through and reach the desired temperature.

Flange

The flange of a circulation heater is made of highly durable metal that has a low coefficient of thermal expansion. A “U” shaped tube is welded into the pipe flange with a thermowell installed in its center, which contains a sensing bulb. Flanged circulation heaters have drilled and tapped holes for ease of installation.

Mounting

In the majority of cases, circulation heaters are mounted vertically or horizontally. The form of mounting is dependent on preference and available space. Factors that have to be considered during mounting are temperature sensors and wiring as well as ensuring that the heating elements are submerged for in-line direct circulation heaters.

Temperature Sensors

Temperature sensors for circulation heaters are resistance temperature detectors or thermocouples in the outlet line. The various types of temperature sensors include element skin sensors, tube sheet sensors, terminal box sensors, vessel body sensors, and process fluid sensors. Sensors used for a system are in accordance with the area of installation.

Heater Bundle or Elements

U shaped heating elements supported by baffles and tie rods deliver the heat and maintain temperature with a pressure drop within safe limits. Heating elements are fixed to the flange in three possible ways, which are direct welding, standoff sleeve pipes, or threaded couplings. The heater bundle can be divided into banks according to process conditions, a factor that allows for better control of the heater’s operation.

Control Panel

As with other industrial tools, control panels for circulation heaters are an interface that allows operators to adjust settings and monitor heating to ensure safe operations. Control logic can take several forms, including contactor, regulated, or a combination of contactor and regulated. Each type of circulation heater control panel has indication systems aside from the standard on and off control.

Circulation heater units are normally enclosed in insulation to prevent heat loss. They are built in accordance with American Society of Mechanical Engineers (ASME) codes for boilers and pressure vessels. Circulation heaters can withstand pressures of 300 lb. up to 600 lb.

How Circulation Heaters are Used

Circulation heaters are efficient and adaptable heating devices that have found wide industrial use. The advent of industrial heaters is due to the many advancements in heating methods and technologies required by modern manufacturing. The precision and reliability of circulation heaters have made them an important tool for a variety of applications.

Chemical Processing

In the chemical industry, the flexibility and durability of circulation heaters enable them to maintain temperature controls for corrosive fluids. The ability of circulation heaters to resist and withstand chemical reactions ensures the safety of processes like distillation, polymerization, and solvent recovery. The outstanding feature that makes circulation heaters so popular is their delivery of precise and consistent heating, which helps maintain product quality and performance.

Oil and Gas

The widest use of circulation heaters is found in the oil and gas industry where they are used to enhance oil’s viscosity and flow characteristics for refinery and transport efficiency. A key part of the use of circulation heaters for the oil and gas industry is their use in removing impurities during processing. As may be assumed, precision temperature control is a necessity in the oil and gas industry, a factor that circulation heaters easily provide.

Food and Beverage

The food and beverage industry uses circulation heaters to maintain temperatures for pasteurization, cooking, and cleaning following the strict regulations from the Food and Drug Administration (FDA). They provide consistent heat for food safety and preservation of taste. Circulation heaters assist in sterilizing tools, equipment, and the heating of ingredients for precision cooking.

Power Generation

In power generation, circulation heaters are used to preheat boiler feed water and turbine oils, which enhances efficiency and reduces energy consumptions and emissions. A critical factor for turbine oils is maintaining viscosity to ensure easy operation and reduction of wear and tear on equipment. Circulation heaters help in providing reliable power production, lowering maintenance costs, and increasing the lifespan of power generating equipment.

There is a very long list of industries that rely on circulation heaters to provide heat for asphalt, tanks, air, nitrogen, process gases, thermal fluid, water heaters, and more. The efficiency, strength, durability, and precision of circulation heaters differentiate them from other forms of heating methods. They are long lasting, dependable, and a reliable method in helping provide uniform and consistent heat.