Circulation Heaters

----Circulation Heaters.jpgCirculation heaters are powerful, electric inline heaters constructed of a screw plug or flange-mounted tubular heater assembly installed into a mating tank or vessel. Inlet and outlet nozzles in the vessel permit liquid or gas flow into and out of the circulation vessel. Standard design circulation heaters use standard screw plug and flange immersion heaters in order to allow for easy replacement and retrofit. Custom units can be designed to suit.

Durex Industries manufactures circulation heaters, also referred to as "inline heaters", which are used for heating flowing liquids, air, and gases. Non-pressurized or highly pressurized fluids can be heated very effectively using indirect circulation heating. A wide variety of standard designs and custom engineered power ratings, sizes, flow capacities, and options are available to fulfill most any application needs.

Durex Industries is an authorized ASME (American Society of Mechanical Engineers) Section VIII Division 1 Code shop with National Board Repair “R” Stamp capability.  Durex can design and fabricate “U” stamp heaters and vessels up to 3,000 psig MAWP or 1500°F design ratings.

Design Features:

  • Flange circulation heater designs
  • Screw plug circulation heater designs
  • A multitude of standard plug and flange sizes for quick delivery
  • Flanges to 40" and to ANSI Class 2500lb ratings available allowing for power rating from 1kW to 1 MW+
  • Copper, steel, SS and Incoloy® materials available, custom tailored to application requirements
  • Integral thermostats or thermocouples available allowing integral control or temperature monitoring
  • UL & CSA recognized elements to 600VAC available, assures safe and reliable performance
  • CSA Hazloc certified terminal enclosures available ensuring compliance to strict safety standards for hazloc areas

Durex has the engineering, design and manufacturing capability to provide value-added process heating system solutions. Skid mount, control panels and other processing components and instruments such as valves, pumps, blowers, piping, temperature sensors, temperature transmitters and expansion tanks can be provided.


Durex Industries also manufactures heavy duty circulation engine heaters to keep emergency generator engines warm for quick starting.

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Circulation Heater Specifications and Options

Heater and Electrical Enclosure Specifications

Dimensional and electrical data are provided for heaters below for various sizes and configurations. All standard design heaters listed in the flange immersion heater section conform to these specifications.

 

Typical Flange Immersion Heater with a NEMA 1 General Purpose Enclosure
Circulation Heater Enclosure Specification Diagram

 

Circulation Heater Enclosures-Screw Plug


 

Circulation Heater Enclosure-Flange

 

  • Maximum Voltage: 600VAC
  • Wattage Tolerance: +5% -10%
  • Resistance Tolerance: +10% -5%
ANSI Flange Size Enclosure Type Typical Number of Elements Heater Cold Length C
Flange Thickness
D
Bolt Circle Dia.
E
Flange Outer Dia.
F
Bolt Hole Dia.
G
Nr. of Bolt Holes
J
Enclosure Height
K
Enclosure Diameter
L
Enclosure Outer Dia.
N
Hole or NPT Size
3" NEMA 1 3 4" 0.938" 6" 7.5" 0.75" 4 4" 5.5" N/A 1"
NEMA 4 3 4" 0.938" 6" 7.5" 0.75" 4 6" 5.5" 7" 1"
NEMA 7 3 4" 0.938" 6" 7.5" 0.75" 4 6" 5.5" 7" 1"
NEMA 1 w/ Thermostat 3 4" 0.938" 6" 7.5" 0.75" 4 4" 5.5" N/A 1"
NEMA 4 w/ Thermostat 3 4" 0.938" 6" 7.5" 0.75" 4 6" 5.5" 7" 1"
Nema 7 w/ Thermostat 3 4" 0.938" 6" 7.5" 0.75" 4 6" 5.5" 7" 1"
4" NEMA 1 6 4" 0.938" 7.5" 9" 0.75" 8 4" 5.5" N/A 1"
NEMA 4 6 4" 0.938" 7.5" 9" 0.75" 8 6" 5.5" 8" 1"
NEMA 7 6 4" 0.938" 7.5" 9" 0.75" 8 6" 5.5" 8" 1"
5" NEMA 1 6/9 4" 0.938" 8.5" 10" 0.88" 8 4" 6.5" N/A 1"
NEMA 4 6/9 4" 0.938" 8.5" 10" 0.88" 8 6" 6.5"
9" 1"
NEMA 7 6/9 4" 0.938" 8.5" 10" 0.88" 8 6" 6.5"
9" 1"
6" NEMA 1 12/15 4" 1" 9.5" 11" 0.88" 8 4" 7.63" N/A 1 1/8"
NEMA 4 12/15 4" 1" 9.5" 11"
0.88"
8 6" 7.63"
10" 1 1/2"
NEMA 7 12/15 4" 1" 9.5" 11" 0.88" 8 6" 7.63" 10"
1 1/2"
8" NEMA 1 18/24 6" 1.125" 11.75" 13.5" 0.88" 8 6"
9.63" N/A 1 1/8"
NEMA 4 18/24 6"
1.125"
11.75" 13.5" 0.88" 8 6" 9.63"
11.5" 1 1/2"
NEMA 7 18/24 6" 1.125"
11.75" 13.5" 0.88" 8 6" 9.63"
11.5" 1 1/2"
10" NEMA 1 27/36 6" 1.188" 14.25" 16" 1" 12 6" 11.63" N/A 1 1/8"
NEMA 4 27/36 6" 1.188" 14.25" 16" 1" 12 7" 11.63" 13.5" 1 1/2"
NEMA 7 27/36 6" 1.188" 14.25" 16" 1" 12 7" 11.63" 13.5" 1 1/2"
12" NEMA 1 36/45 6" 1.25" 17" 19" 1"
12 6" 13.75" N/A 1 1/8"
NEMA 4 36/45 6" 1.25"
17" 19" 1" 12 7" 13.75"
15.75" 1 1/2"
NEMA 7 36/45 6" 1.25"
17" 19" 1" 12 7" 13.75" 15.75"
1 1/2"
14" NEMA 1 45/54 6" 1.325" 18.75" 21" 1.125" 12 6" 15.75" N/A 1 1/8"
NEMA 4 45/54
6"
1.325"
18.75" 21" 1.125"
12 7" 15.75" 17.75" 1 1/2"
NEMA 7 45/54 6"
1.325" 18.75" 21" 1.125" 12 7" 15.75" 17.75" 1 1/2"

Circulation Heater Thermostat Options

Thermostats can be mounted inside of the terminal enclosure to provide inexpensive, local temperature control of the circulation heater and liquid being heated. Process (automatic control) and high limit (manual reset) thermostats are available. Temperature settings are adjustable unless a fixed set point thermostat is ordered. Single pole (SPST) thermostats are typically used for single phase heaters and double pole (DPST) thermostats for three-phase heaters. For high current draw circulation heaters, the thermostats are often wired for "pilot duty" to a user-supplied relay.

----Thermostat.jpg DPST Thermostat

Standard Available Bulb & Capillary Thermostats

Temperature Range Type
Max. Amps to 240VAC Max. Amps
at 480V
0 - 100°F Single Pole (SPST) 20 Amps N/A
85 - 230°F Single Pole (SPST) 20 Amps N/A
120 - 570°F Single Pole (SPST) 20 Amps N/A
0 - 100°F Double Pole (DPST) 30 Amps 21 Amps
60 - 250°F Double Pole (DPST) 30 Amps 21 Amps
100 - 550°F Double Pole (DPST) 30 Amps 21 Amps

Features

  • Single pole (SPST) and double pole (DPST) thermostats available
  • Wide range of temperature selections
  • Optional knob & bezel

Double Pole, Single Throw (DPST)

----DoublePoleThermostats.jpg

Single Pole, Single Throw (SPST)

----SinglePoleThermostats.jpg

Part Number Description Maximum Voltage Maximum Amperage Bulb Length Bulb Diameter Capillary Length
CNTR-TSTAT-CAP-0-100-01 0-100°F SPST 240 V 20 A 3.3" .24" 36"
CNTR-TSTAT-CAP-85-230-1 85-230°F SPST 240 V 20 A 3.3" .24" 36"
CNTR-TSTAT-CAP-120-570-1 120-570°F SPST 240 V 20 A 3.5" .20" 36"
CNTR-TSTAT-CAP-0-100-03 0-100°F DPST 480 V
21 A / pole at 480 V
30 A / pole at 240 V
4.5" .375" 84"
CNTR-TSTAT-CAP-060-250-04 60-250°F DPST 480 V 4.5" .375" 60"
CNTR-TSTAT-CAP-100-550-01 100-550°F DPST 480 V 4.5" .375" 60"

Circulation Heater Temperature Sensor Options

Thermostat or Process SensorProcess Sensors

A thermocouple or RTD sensor probe can be inserted into a thermowell in the heater screw plug or flange to measure process fluid temperature. As an option, the process temperature sensor can be mounted at the outlet of the circulation vessel. Type J and Type K are the most common thermocouple calibrations, while a Pt 100 Ω DIN Curve sensor is the most common RTD used. Type J thermocouples and RTDs are typically used to 1000°F (540°C), whereas Type K thermocouples are used to 2000°F (1100°C) max. Other sensors are available. Standard lead length is 72” (1825mm). Specify sensor type, location and lead length when ordering.

 

High Limit Sensors

Process Sensor Mounted at OutletA thermocouple or RTD sensor probe is fed through the screw plug or flange and clamped directly to a heater element to measure element temperature. This allows monitoring of the sheath temperature to prevent over temperature conditions that may shorten heater life and/or prevent fluid degradation. An alternative is to insert the high limit sensor into a thermowell that is clamped or welded to the heater element sheath. This facilitates easy sensor replacement, but at the expense of a slower sensor response time. The sensor must always be placed on a heater element near the outlet of the circulation heater. Unless otherwise specified, the outlet is assumed to be on the end opposite the electrical enclosure. Contact Durex to ensure the correct sensor placement for your application. Standard lead length is 72” (1825mm). When ordering, specify sensor type, sensor mounting style, location and lead length.


Sensor Options
Type ‘J’ Process T/C
Type ‘K” Process T/C
Type ‘J’ Process T/C (Circulation Heaters - Outlet by Enclosure)
Type ‘K’ Process T/C (Circulation Heaters - Outlet by Enclosure)
Type ‘J’ Sheath High Limit T/C
Type ‘K’ Sheath High Limit T/C
Type ‘J’ Sheath High Limit T/C (Circulation Heaters - Outlet by Enclosure)
Type ‘K’ Sheath High Limit T/C (Circulation Heaters - Outlet by Enclosure)
Type ‘J’ Process AND High Limit T/Cs
Type ‘K’ Process AND High Limit T/Cs
Type ‘J’ Process AND High Limit T/Cs (Circulation Heaters - Outlet by Enclosure)
Type ‘K’ Process AND High Limit T/Cs (Circulation Heaters - Outlet by Enclosure)
Type ‘J’ Process T/C Outlet Nozzle (Circulation Heaters)
Type ‘K’ Process T/C Outlet Nozzle (Circulation Heaters)
Type ‘J’ Process T/C Outlet Nozzle (Circulation Heaters - Outlet by Enclosure)
Type ‘K’ Process T/C Outlet Nozzle (Circulation Heaters - Outlet by Enclosure)
Type ‘J’ Process T/C Outlet Nozzle AND High Limit T/C
Type ‘K’ Process T/C Outlet Nozzle AND High Limit T/C
Type ‘J’ Process T/C Outlet Nozzle AND High Limit T/C (Circulation Heaters - Outlet by Enclosure)
Type ‘K’ Process T/C Outlet Nozzle AND High Limit T/C (Circulation Heaters - Outlet by Enclosure)
Contact Durex for special temperature sensor requirements

Circulation Heater Construction Options

Custom Voltage and Power Rating - A large variety of standard design heaters are available on the following catalog pages. However, custom volts, watts and watt density designs are available upon request.

ANSI Flange Configuration - ANSI Class 150 lb. flanges are available standard from 3”to 14”. Smaller sizes such as 2” and 2 ½”, as well as, larger sizes up to 40” can be provided. Class 300 lb. and Class 600 lb. flanges can be supplied with minimal lead time effect; up to Class 2500 lb. are also available. Steel, 304 Stainless Steel and 316 Stainless Steel flange materials are standard, although other materials can be ordered upon request.

Vessel Configuration - Standard design circulation vessel (also called “chamber” or “tank”) configuration is schedule 40 carbon steel pipe unless otherwise stated, and is pressure tested to 150 psig to ensure integrity. Heavier wall pipe (schedule 80, 160, etc.) is available for higher pressure and temperature applications. Other materials such as 304 Stainless Steel and 316 Stainless Steel are also readily available. Steel vessels are primer-coated unless otherwise specified.

Inlet & Outlet Nozzles - Up to 8” vessel sizes, the standard design nozzle is a male NPT (National Pipe Thread). For 10” and larger heater vessels, 150 lb. ANSI flange nozzles are standard. Other nozzle sizes, thread types, and flange classes (300 lb, 600 lb, etc.) are available.

Heater Element Sheath Material - Copper, steel, 304 Stainless Steel, 316 Stainless Steel and Incoloy® 840 materials are standard. Also available are Incoloy® 800, 321 Stainless Steel, Inconel®, etc. Seamless and heavy wall construction for higher pressure and/or corrosive fluids can be provided as well for extended heater life.

Unheated (Cold) Length - The unheated (cold) length can be varied to suit application requirements. Longer unheated sections are often used to keep the termination area cool or to focus heat generation in a specific area of the media being heated.

Circulation Heater Enclosure DiagramStand-Off Enclosures - The electrical enclosure is separated from the flange by a six inch air gap to lower the ambient temperature of the electrical wiring in the enclosure. This option is recommended whenever the flange temperature is expected to exceed 400°F (200°C).

CSA Certified Enclosures - CSA certified explosion resistant electrical enclosures are certified to Class 1, Div. 1 & 2, Groups B, C & D hazardous locations. Specify the hazardous location classification requirement, process temperature, maximum ambient temperature, maximum working pressure of application, media being heated and heater mounting orientation (horizontal or vertical).

ASME Code Stamp & CRN Certification - For higher pressure and/or temperature applications, Durex Industries is also an authorized ASME (American Society of Mechanical Engineers) Section VIII Division 1 Code shop with National Board Repair “R” Stamp capability.  Durex can design and fabricate “U” stamp heaters and vessels up to 3,000 psig MAWP or 1500°F design ratings. Canadian Registration Numbers (CRN) for Canadian Province requirements for pressurized circulation heaters can be obtained as needed.

Sheath Treatment and Finish - For pharmaceutical and other “clean” applications, a bright anneal finish can be supplied. Also available, depending on configuration, are passivation and electro-polishing which remove any free iron and also provides a smoother surface finish both on the heater element as well as the screw plug fitting.

Circulation Heater Direction of Flow DiagramFlow Baffles - For circulation applications, flow baffles are employed to induce cross flow over the heater elements thereby improving heat transfer from the heater elements to the flowing fluid. However, the trade-off is increased pressure drop across a circulation heater. Contact Durex for more information and assistance.

Insulation & Shroud - All standard design circulation heaters are wrapped with 1” of mineral wool insulation and protected by a heavy duty sheet steel metal shroud. Thicker insulation, other insulation materials and fully welded (weatherproof) shroud assemblies are available.

Seal Options

Silicone Conformal Coating – Standard on catalog units, this seal provides general moisture / contamination protection to 220°F (105°C). However, it is porous and will allow moisture penetration over time. Not recommended for storage or use in high humidity environments.

Silicone RTV – Offers improved moisture and contamination protection to 400°F (200°C). However, it is also porous and will allow moisture ingress over time.

Epoxy Seal – Offers the best moisture and contamination protection of these seal choices. Rated for 450°F (230°C),this seal has low porosity and is recommended for higher temperature applications, high moisture environments and where long term storage is foreseen.

How to Order Durex Circulation Heaters

To place an order, or get a quotation, please provide the information itemized below or contact Durex Industries for further assistance.

Electrical Rating - Voltage, phase, Wattage

Heater / Vessel Configuration - Screw plug (or ANSI flange) pipe size, pressure rating and material (Steel, 304 Stainless Steel, 316 Stainless Steel or other); inlet/outlet size, location/orientation on vessel, and connection type (pipe thread or flange).

Element Sheath Material - Copper, Steel, 304 Stainless Steel, 316 Stainless Steel, Incoloy® or other.

Element Diameter and Quantity - Provide element diameter and quantity (or indicate if Durex should advise).

Element Watt Density - 8, 16, 23, 48 or 60 W/in2, or other watt density value

Immersion Length - Provide desired immersion length or maximum allowable length, and cold length if non-standard.

Seal Options - Silicone conformal coating (standard), RTV or epoxy.

Electrical Enclosure - NEMA 1(standard), NEMA 4, NEMA 7, NEMA 4/7 or CSA Certified. Please designate hazardous location information if a certified enclosure is required. Also indicate if a stand-off enclosure is required.

Sensing & Control - None (standard), thermostat type (SPST or DPST, process or high limit manual reset) and range; process sensor (thermocouple or RTD type and sensor location – standard or at outlet) or/and high limit sensor type.

Insulation and Shroud - Standard (1” thick mineral wool with sheet metal shroud), no insulation, other insulation thickness or type, shroud type (standard or weatherproof) and shroud material.

Other Configuration Details - Sheath treatment requirements, flow baffles & spacing, paint requirements, special design or testing requirements, etc.

 

Circulation Heater Standard Parts List

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Circulation Heater Application Guidelines

The goal is to optimize the heater configuration to ensure the longest life possible while minimizing overall product and life cycle costs. The general temperature, sheath material and watt density guidelines below can aid in proper circulation heater selection for some common liquids. Contact Durex for further assistance.

Liquid Maximum Operating Temperature °F (°C) pH Level and/or Concentration Recommended Sheath Material Typical Plug or Flange Material Maximum Watt
Density W/in2
(W/cm2)
Clean, Potable Water 212 (100) Neutral (pH 6 to 8) Copper Brass 60 - 90 (9.5 - 14)
Process Water & Weak Solution 212 (100) pH 5 to 9; 2-3% Incoloy® or 304SS Steel or 304SS 48 (7.5)
Demineralized,
Deionized Water
212 (100) Neutral 304SS or 316SS (passivated) 304SS or 316SS 60 (9.5)
Weak (Acidic) Solutions* 210 (100) Up to 5-6% Incoloy®, 316SS Steel 48 (7.5)
Mildly Corrosive
(Acidic) Solutions*
180 (80) 5-15% Incoloy®, 316SS 304SS or 316SS 20 - 23 (3.5)
Severely Corrosive
(Acidic) Solutions*
180 (80) >15% Incoloy®, titanium, Teflon® 304SS or Other 15 - 16 (2.5)
Caustic Soda 10% 210 (100) pH 14; 10% Incoloy® Steel 20 - 23 (3.5)
Caustic Soda 50% 250 (120) pH 14; 50% Incoloy® Steel 16 (2.5)
Fuel Oil 1 & 2; Kerosene
Lube Oil SAE 10 to 30
200-250 (95-120) - Steel Steel 20 - 23 (3.5)
Fuel Oil 4 & 5;
Lube Oil SAE 40 to 50
200-250 (95-120) - Steel Steel 15 - 16 (2.5)
Fuel Oil 6 & Bunker C 160 (70) - Steel Steel 6 - 8 (1.2)
Hydraulic Oil 100 (40) - Steel Steel 15 - 16 (2.5)
Ethlyene Glycol 300 (150) - Steel Steel 23 - 30 (3.5 - 4.5)
Glycerine 500 (260) - Incoloy® Steel 8 - 10 (1.5)
Molten Salt Bath 800 (425) - Steel, 321SS, Monel® Steel 23 - 30 (3.5 - 4.5)
Paraffin Wax 150 (65) - Steel or 304SS Steel 15 - 16 (2.5)
Molasses 100 (40) - 304SS or 316SS 304SS 4 - 5 (0.7)

*Sheath material and watt density dependent on type of acid, concentration, temperature, aeration, movement, etc.

Please note that the user accepts full responsibility for validating that a heater is suitable for a given liquid or gas heating application and that it is properly instrumented and controlled. Durex HIGHLY RECOMMENDS the use of a thermostat or temperature controller AND a high limit sensor with an FM-approved safety controller to prevent unexpected over temperature conditions. This is a requirement for DFX Cast Circulation heaters.

For DFX Cast Circulation heaters, use the recommended watt density limits as the maximum effective watt density on the interior surface of the DFX flow tube. Whereas traditional circulation heaters can be mounted vertically or horizontally, DFX Cast Circulation heaters MUST BE INSTALLED VERTICALLY. This prevents the formation of vapor pockets that could inhibit flow as well as lead to localized overheating of the heater body.

Follow instructions on Installation & Maintenance manuals completely. Contact Durex with any questions and for further assistance.

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typical circulation heating applications

  • Air and Similar Gases
  • Catalyst (re)Activation & Dehumidification
  • Caustic Solution Heating
  • Storage Tanks
  • Fuel Oil Preheaters
  • Heat Transfer Systems
  • Hydraulic and Heat Transfer Oils
  • Hydrocarbon gases
  • Lube Oil & Fuel Oil Heating
  • Lubrication & Conditioning Systems
  • Oil Suction Heaters
  • Process Air & Gas Heating
  • Process Chemical Reactors
  • Steam Superheating
  • Water-Glycol Solution Heating

 

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