Energy Efficient Selection of Steam-to-Liquid Heat Transfer Systems

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Engineered Steam-to-Liquid Heat Transfer Systems

Traditionally, the engineering of steam-to-liquid heat transfer systems has been done by using the maximum available steam pressure to select the smallest and least expensive heat exchanger. The control valve, steam trap and other ancillary equipment would then be selected using the operating conditions of this heat exchanger. While this method works, there is a better way.

It is now possible to reduce both initial equipment costs and operating costs. This is done by selecting the components of the entire system at the same time. Your ITT R&CWG Representative can now optimize your steam-to-liquid heat transfer systems with each component working together in a manner that optimizes the system as a whole.

Optimizing The System As A Whole:
Let’s take an example. Say we have 90 psig steam pressure available for a heat transfer application and use a low pressure drop control valve—10 psig ÆP—to select a heat exchanger with minimal size and surface area.

At a high steam operating pressure, there is less latent heat available for the heat exchanger, while downstream of the heat
exchanger, a higher percentage of flash steam is produced. This flash steam results from re-evaporation of the condensate when it is exposed to lower pressure or vented return lines.

In this type of system, a flash tank may be required to handle this re-evaporation, and high temperature condensate return systems may be required to pump the condensate discharging from the flash tank.

The net result of using high steam pressure at the heat exchanger is flash steam losses causing wasted energy ($), lower system efficiency ($$), and extra equipment to handle higher temperature returns ($$$). But we did save initial costs by selecting the smallest heat exchanger....? Not necessarily!

When we re-select the same application but use a steam pressure regulator to reduce the steam pressure at the heat exchanger to 5 psig, the size of the heat exchanger will increase. However, the heat exchanger cost is only part of the system cost.

By reducing steam pressure at the heat exchanger, the steam control valve may decrease in size, lowering its initial cost. Also, the steam trap may become lower in cost because of the reduced operating pressure. By lowering your steam pressure, the result may be a net savings on your initial equipment cost.

But there’s more. By using the reduced steam pressure of 5 psig, we have more latent heat available in the heat exchanger, and thus a lower percentage of flash steam. This may allow for elimination of the flash tank and conversion of the high temperature condensate return unit to a lower cost, conventional condensate return unit.

The net result: lower initial costs—and most importantly, lower operating costs yielding annual cost savings that greatly increase payback. See the example below for a typical
comparison.

Your ITT R&CWG Representative can select an engineered steam-to-liquid heat transfer system that operates efficiently, effectively, and possibly at a lower initial cost because they fully understand all of the critical components involved.

Your ITT R&CWG Representative handles Bell & Gossett heat exchangers, pumps and air control equipment; Hoffman steam control valves, regulators, safety valves, steam traps, vacuum breakers and strainers; and Domestic condensate return and boiler feed pumps. Count on your representative for the right combination of training, expertise and tools to pull it all
together in a system that suits your application exactly, using the award-winning ESP-PLUS system evaluation and equipment selection program.

Using our example steam pressures, let’s assume our heat exchanger requires 3,000 lbs/hr of steam, operates 14 hours a day for 250 days per year and the condensate goes to a vented condensate receiver at 0 psig atmospheric pressure. We will assume our steam costs $6.50 per 1000 lbs.

NET ANUAL SAVINGS FROM REDUCING PRESSURE
1,071,000 lbs of steam or $6,961.00

Specifications For:
Furnish and install according to manufacturer’s instructions, one ITT Fluid Handling energy efficient steam-to-liquid heat transfer component system, which shall have the capacity to heat _________ GPM of _________ (fluid) from _________ °F (temperature) to _________ °F (temperature) when supplied with _________ psig saturated (or degrees superheated) steam to the steam regulator. The heat exchanger shall be sized for maximum _________psig inlet pressure. The system is to have a maximum of _________ % flash steam. Energy loss calculations shall be furnished to the engineer for approval and shall include annual dollar operating costs at design conditions.

The energy efficient steam heat exchanger component system shall be piped in the field with all necessary valves, pipe and fittings, according to plans and specifications and shall consist of the following major components:

1. Hoffman Series 2000/1140 (pneumatic or self-contained) modulating steam control valve.
2. Hoffman F&T trap and “Y” strainer for the drip leg.
3. Bell & Gossett “SU” type heat exchanger with _________ fouling factor, ASME constructed with signed U-1 form per heat exchanger specification.
4. Hoffman vacuum breaker for the heat exchanger.
5. Hoffman "Y" Strainer and F&T Trap for the heat exchanger. (F&T Trap size based on 0.5 psig differential pressure with 1.5 min. safety factor.) Trap installed a minimum of 15" below the heat exchanger.
6. Optional components
   • _________ steam safety relief valve
   • _________ gauges, high pressure cocks and pigtails
   • _________ thermometers
   • _________ Bell & Gossett circulating pumps for liquid (primary/secondary) system with flow measuring and balancing valves
   • _________ ASME relief valve for system liquid.
   • _________ factory piped and frame mounted construction or individual components shall be specified.
7. __________ Duplex Domestic/Hoffman condensate return unit with accessories.

Single source system responsibility requires all major components to be supplied by a single source manufacturer.

©1992 ITT Corporation Printed in U.S.A. 11/92
Posted by permission from ITT Residential & Commercial Water Group
**NOTE: This article was originally published under the name ITT Fluid Handling. Where appropriate, the name has been edited to ITT Residential Commerical & Water Group, reflecting the current name of this subdivision of ITT Corporation.