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Heat Exchanger Technology

Monday, February 23, 2009

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Oil - Fouling Factors in [m2K/W]


Oil Type
Fouling Factor

Gasoil0.00009

Transformer0.00018

Lubrication0.00018

Heat Transfer oil0.00018

Hydraulic0.00018

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posted by Webworm, 2:18 PM | link | 0 comments |

Sunday, February 22, 2009

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Gas / Vapor - Fouling Factors in [m2K/W]


Gas / Vapor Type Fouling Factor

Hydrogen0.00176

Engine exhaust0.00176

Steam0.00009

Steam with oil traces0.00018

Cooling fluid vapours with oil traces 0.00035

Organic solvent vapours0.00018

Compressed air0.00035

Natural gas0.00018

Stable top products0.00018

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posted by Webworm, 1:53 PM | link | 0 comments |

Saturday, February 21, 2009

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As the price of electricity, natural gas and other fossil fuels continues to climb, chemical processors are more closely examining high-temperature operations and heat-transfer systems to see if more efficiency can be had. In many cases
it can, and, as a result, heat-transfer projects are not only justifiable, but downright attractive.

There was a dialog among a few heat exchanger specialist from Alfa Laval, Paul Muller, Exergy LLC, etc. The dialog mainly discussed on strategy to improve heat transfer efficiency, heat recovery and efficient process control during this high energy price arena.

A few tips have been present :
  • The energy crisis results high prices all of the time shorten paybacks. Energy efficient is one of the way to minimize cost
  • Energy efficient heat transfer equipment such as Plate Heat exchanger, Gasketed Heat exchanger, Bonded Heat exchanger, etc is one of the option.
  • For a service using Shell & Tube (S&T), the overall heat transfer coefficient (HTC) is around 300 Btu/h ft2°F. However, the overall heat transfer coefficient (HTC) for a compact heat exchanger can be improved 3-4 times (~1000 to 12000 Btu/h ft2°F).
  • With higher overall heat transfer coefficient, this may translate into less space, smaller installation and handling cost.
  • Gasketed Heat exchanger good for maintenance. However shall take additional attention on the compatibility between gasket and fluid.
  • All welded or Bonded heat exchanger may be considered if there is gasket & fluid compatible problem
  • For laminar flow, heat transfer rate is only the function of fluid thermal conductivity. Operate heat transfer equipment at laminar flow during turndown could significantly reduce it heat transfer rate
  • Compact heat exchanger promote turbulence. High turbulence increase heat transfer rate and reduce fouling
  • Thus plant releasing hot exhaust gas from burner, boiler, gas turbine, etc to atmosphere may take the opportunity to recover heat
  • Improve temperature control in process system would reduce energy usage
Download details discussion...Registered CE subscriber only
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posted by Webworm, 3:23 PM | link | 0 comments |

Wednesday, February 18, 2009

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Tubular Exchanger Manufacturers Association (TEMA) has developed a series of fouling factor for Shell and Tube (S&T). These fouling factor are generally higher than Plate Heat Exchanger (PHE), why not use S&T fouling factors to size PHE ?

Isn't this approach conservative and guarantee the performance ?

Reason being...
  • Oversized Plate Heat Exchanger (PHE) required extra CAPEX and extra Space for oversized PHE
  • Tubulence minimise fouling tendencies in correctly sized PHE. Oversized PHE results low actual velocity and increase potential fouling and inefficient heat transfer
  • HTRI studies showed PHE fouling significant lower than Shell & Tube Heat Exchanger (S&T)... factor of 6.7
GUIDELINE : Do not oversized PHE more than 25% against required area.

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posted by Webworm, 12:14 PM | link | 0 comments |

Tuesday, February 17, 2009

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WATER - Fouling Factors in [m2K/W]

Water Type Tcw < 50 ° C
Tf < 120 ° C
Tcw > 50 ° C
Tf > 120 ° C

v < 1 m/s
v > 1 m/s v < 1 m/sv > 1 m/s
Sea0.000090.000090.000180.00018
Brackish0.000350.000180.000530.00035
Cooling tower with inhibitor0.000180.000180.000350.00035
Cooling tower without inhibitor 0.000530.000530.000880.00070
City grid0.000180.000180.000350.00035
River mimimum0.000180.000180.000350.00035
River average0.000530.000350.000700.00035
Engine jacket0.000180.000180.000180.00018
Demineralized or distilled0.000090.000090.000090.00009
Treated Boiler Feedwater0.000180.000090.000180.00018
Boiler blowdown0.000350.000350.000350.00035

Tcw = Water temperature
Tf = Fluid temperature
v = Water velocity

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posted by Webworm, 2:16 PM | link | 0 comments |
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hitran_flow


In one the recent depleted field debottlenecking project, new Booster Compression unit will be installed to boost the depleted well fluid pressure to meet high delivery pressure while maintaining the production forecast market demand. As this unit will be installed on existing platform, space and weight constraint are the major issues. Many efforts have been implemented in order to reduce new installation space and weight. One of them is to reduce the Lube Oil Cooler Size. One of the question raised.

How to reduce lube oil cooler size while meeting duty and flow ?

The following image demonstrates a wire matrix turbulator by hiTRAN

inkflow

Wire matrix turbulator, known as a HiTRAN® Matrix Element, is inserted into inner tube of Heat Exchanger. The basic principle is to promote fluid mixing, convert laminar flow to turbulence flow pattern, maintaining turbulence flow pattern and improve tube-side heat transfer.

From above image,
- region (A) is laminar flow conditions
- region (B) is turbulence caused by the use of hiTRAN matrix tube Inserts

Case Studies
See below the comparison between Compressor lube oil cooler (Air-Cooled Heat Exchanger) with and without turbulator :

  • Number of tube rows above each other : 5* (with turbulator) 10* (without turbulator)
  • Width : 4* m(with turbulator) 7.3* m (without turbulator)
  • Length : 7.9* m (with tubulator) 12.2* m (without turbulator)
  • Height : 7.2* m (with turbulator) 9.3* m (without turbulator)

* For reference only

Turbulator has significantly reduce the space consume and weight and it ensure the project to proceed to installation phase. Idea of using turbulator is one of the success story in debottlenecking project especially those have space and weight constraints.

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posted by Webworm, 1:53 PM | link | 0 comments |

Monday, February 16, 2009

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Product fluid in reactor involve exothermic process is commonly hot. It is then sent to distillation and separation system for catalyst and raw material recovery. Separated product is then cooled by plant wide Cooling Water (CW) before it is sent to storage tank. The product temperature will have to be maintained.

How this temperature is controlled ?


Temperature Control Methods

There are several ways to maintain the product temperature :
  1. Provide a product bypass across the Cooler, control valves on Product bypass line and Outlet line (Split range control) with fixed CW flowrate
  2. Provide a CW bypass across the Cooler, control valves on CW bypass line and CW inlet to Cooler with full product flow across cooler
  3. Provide a CW bypass across the Cooler, control valves on CW bypass line and CW outlet to Cooler with full product flow across cooler
  4. Provide a Control valve at the Cooler inlet with full product flow across cooler
  5. Provide a Control valve at the Cooler outlet with full product flow across cooler

Generally the product flow is fixed by operator based on production plan and the product flow shall not be controlled. Thus, it is always not recommended to provide a control valve at the inlet and outlet of product line for product temperature control.

Disturbance of CW Network Balance
Cooling water is in a network supplying to many heat exchanger through out the plant for cooling purpose. It is normally supplied by a set of centrifugal pump. As centrifugal pump head will be affected flow across, any changes in the CW demand will affect the CW balance in network. This will further affect the pressure in the network and hence the CW flow into other heat exchangers. Thus, it is always recommended not to throttle the CW flow as much as possible to avoid CW balance.

Scaling
Throttling CW flow into heat exchanger would potential lead to low CW flow into heat exchanger, high film temperature at on CW side and promote scaling. The option (ii) and (iii) are always recommended IF throttling on CW side is chosen.

Potential affecting Production
Controlling product fluid temperature with product bypass across the Cooler, control valves on Product bypass line and Outlet line (Split range control) and fixed CW flowrate (option i) is one of the common way in temperature control for product cooling. As it minimize the impact to CW network. Nevertheless, there is still concern about manipulating product fluid or mal-operation (controller failure) of control valves would potentially lead to production lost, the option (ii) and (iii) are always the recommended option.

CW Pressurise or Non-Pressurise
Option (ii) and (iv) compare to option (iii) and (v), the difference is the location of main CW line control valve (either at the inlet or the outlet). Providing a control valve at the outlet will have the following advantages :


a) Maintain high pressure in the heat exchanger and higher pressure will results higher heat transfer

b) CW at high pressure will minimise potential of boiling

c) CW at high pressure will minimise potential release of dissolved gases in CW , trap in heat exchanger and reduce heat transfer

d) In event of Control valve failure (failed to full close position), not further Cooling. CW in the heat exchanger will be heated and potentially lead to heat exchanger overpresure due to thermal expansion and/or boiling. The CW will be relieved via Pressure Relief Device provided on the heat exchanger. Providing control valve at the outlet would allow continue CW feeding into the heat exchanger, this minimise the potential of sudden temperature increase and cause heat exchanger due to thermal shock. The downside is release CW into disposal network.

Considering above advantages, it is always recommended to provide control valve on CW line at the outlet IF throttling CW side is chooses.

CONTROLLING SHELL AND TUBE EXCHANGERS
"Controlling Shell & Tube Heat Exchanger", an excellent article by Walter Driedger discussed about all type of control schemes around heat exchanger. Check out.

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posted by Webworm, 3:07 PM | link | 2 comments |