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Low pressure steam is wasted in most of industrial plants. The condensing system needs electricity. Proposed method needs zero energy.


Description

Summary

Many processing plants use steam.  Based on U.S. Department of Energy estimates, over 45% of all fuel burned by U.S. manufacturers is consumed to raise steam (DOE Best Practices).

Steam is used in many applications including driving steam turbines, providing process and space heating and is even used as a feed in hydrogen or methanol production processes.

Industrial plants are generally serviced by a steam system consisting of three main networks each at a distinct pressure. These networks are internally labeled as the high pressure (150 psig and above), medium pressure (40 to 150 psig) and low pressure (Below 40 psig) systems. Along with these, a condensate recovery system operates to capture and return condensate to be reused to make more steam. Figure 1 shows a typical steam system consisting of a steam generator, steam consumers and a condensate recovery system.

 

Figure 1- Steam system distribution in a typical plant

High pressure steam is used by industrial plants because of the high energy content in each pound of steam. However, oftentimes steam is generated at higher pressures or in larger volumes than needed at a particular time. These inefficiencies may lead steam systems to let down high pressure steam to a lower pressure or to vent excess steam to the atmosphere. Many plants those produce and use high pressure steam end up with a high volume of low pressure steam that has insufficient energy to be of further use.  Consequently, these plants struggle to find ways to either use or recover the remaining energy in the low pressure steam.

Air-cooled steam condensers have been used by industry since the 1930s to condense and reuse extra steam. 


What actions do you propose?

Compare Conventional and Recommended Steam Condensing Systems

A typical conventional steam condensing arrangement is shown in Figure 2. The system includes an A-frame air-cooled steam condenser, non-condensable removal unit, condensate storage tank, and a pump to return the condensate to the steam generation plant.

The conventional steam condensing system uses electrical motors to drive blowers, condensate pumps and vacuum pumps. This increases both demand and energy charges for a plant over the time and raises the annual utility power bill. Therefore in most cases industries intend to vent their low pressure steam to the atmosphere instead of making condensate that ends up with high electricity cost. Moreover electricity transmission to the place that steam condensing unit will be located makes another constrain. 

Figure 3 shows a schematic of recommended steam condensing system. This system is made up of three main steam driven equipment items including a blower to provide cooling air, a pumping trap to return the condensate to the boiler and a steam eductor to separate any non-condensables.  As shown in Figure 3, excess steam can be used to drive the system components instead of electric motors.

  1. Condenser blower: a steam turbine will be used instead of an electric motor to provide the required shaft work.
  2. Vacuum system: to provide the vacuum needed to remove non-condensables a steam ejector will be installed.
  3. Condensate pump: using a pumping trap instead of a conventional motor driven pump, stored condensate will be returned to steam generation boiler. A pumping trap (See Figure 4) is a mechanical device that uses a small amount of low pressure steam to pressurize the condensate sufficiently to return it to the boiler for reuse.

 

The condensate stream leaving the air cooler is sent through a heat exchanger to condense all the steam exhausted from the blower steam turbine and the vacuum ejector. The condensate temperature that leaves the air cooler is low enough to be used in the heat exchanger with no evaporation.

 

The collected hot condensate (temperature may be as high as 225°F) is pure enough that it can be routed directly as is to the boiler feed water tank without further water treatment to be reused in steam generation process.  As an example, a typical conventional water treatment plant consumes sulfuric acid, caustic soda, sodium aluminate, lime and electricity to purify raw water from a public utility or other source.

As industrial scale of all needed equipments for this purpose is available in marketplace, developing of this system is realistic.

Figure 2- A simplified process flow diagram of conventional steam condenser

Figure 3- A simplified process flow diagram of recommended steam condenser

Figure 4- A schematic of pumping trap

An air-cooled A-frame steam condenser is used to condense excess low pressure steam in this process. The A-frame condenser system includes the bundles, steam distribution manifold, fans, motors and supporting steel. Figure 5 shows a schematic of A-frame air-cooled steam condenser system.

Figure 5- A-frame air-cooled steam condenser unit

 


Who will take these actions?

Any plant that uses steam in its processes can take advantage of this system. Power plants, oil refineries and petrochemical plants use a very large amount of steam.


Where will these actions be taken?

This action can occur worldwide however, developed countries have best potential.


How much will emissions be reduced or sequestered vs. business as usual levels?

N/A


What are other key benefits?

Running steam system condensing unit will be more economical as the utility cost will be negligible.


What are the proposal’s costs?

N/A 


Time line


Related proposals

No related proposal.


References

N/A