Venting Steam in Fluid Heating Processes

Equipment and procedures can help mitigate steam loss for better sustainability
[ Page 1 of 5 ]       
Provided by Process Heating

Learning Objectives:

  1. Discuss ways in which flash steam, utility steam, blowthrough steam and low pressure non-utilized steam can be mitigated.
  2. Describe the difference between modulating and non-modulating steam systems in plant operations.
  3. List some precautions and hacks for thermal fluid operations to avoid flashing moisture off into concentrated steam.
  4. Discuss the two types of steam audits professionals use to evaluate a boiler system.

Credits:

1 PDH
0.1 IACET CEU*
1 AIA LU/Elective
1 PDH*
BNP Media has met the standards and requirements of the Registered Continuing Education Program. Credit earned on completion of this program will be reported to RCEP.net. Certificates of Completion will be issued to all participants via the RCEP.net online system. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the RCEP.
This course may qualify for continuing education through the NYSED. For further information, please visit the NYSED website at http://www.op.nysed.gov/prof/pels/peceques.htm.
This course may qualify for continuing education through the FBPE.

Plants need efficient steam-venting systems to reduce costs and emissions. These articles spotlight various ways steam systems fail and offer insight into what equipment and procedures can help mitigate and prevent venting problems in order to increase a steam system’s thermal-cycle efficiency.

Venting Steam: The Largest Energy Loss in Steam Systems

By Kelly Paffel

With today’s competitive international market, all plants need to reduce operating costs, and lowering energy consumption can have a positive impact on the bottom line. A plant’s steam and condensate systems cannot afford to vent any utility steam, blowthrough steam or flash steam to the atmosphere. An additional benefit of not venting steam is a significant reduction in emissions in the boiler operation.

Any steam venting from the steam and condensate system is the top reason for lost energy in today’s steam systems. Can this objective be accomplished? Yes. Many plants have accomplished the goal of not venting steam, and they were rewarded with a high steam system thermal-cycle efficiency.

Of course, lowering energy costs also makes the plant more profitable and better able to compete in today’s international market.

Why Do Plants Vent Steam to the Atmosphere?

There are several reasons that plants vent steam to the atmosphere. With modifications using today’s technology, however, steam and condensate systems do not need to vent steam.

Venting Steam: The Largest Energy Loss in Steam Systems

Unbalanced header pressure can be caused by instantaneous process changes, steam turbine operation, and uncontrolled pressure-reduction stations.

Improper or No Steam Balancing of the Steam System. The steam balance is always the first necessary part in any steam system optimization and management program. The valuable knowledge gained from a steam balance can help plant engineers use the steam system in the most efficient way, and this knowledge also provides essential insight that can support efforts to increase the steam system’s thermal-cycle efficiency. The perfect steam balance has no energy losses from steam venting, excessive low pressure steam venting, flash steam venting, condensate loss, and so on.

However, a high percentage of plants do not have a steam balance program, which typically leads to the following results:

  • Flash steam being vented.
  • Utility steam being vented to meet the process steam demands.
  • Blowthrough steam vented from the process blowthrough; bypass valves opened; and steam trap station failures.
  • Low pressure nonutilized steam.

Venting Steam: The Largest Energy Loss in Steam Systems

A small amount of flash steam being vented to the atmosphere has a significant energy loss.

Ideally, every plant should strive to achieve the highest steam thermal-cycle efficiency possible. The steam balance provides the information needed to achieve this goal (table 1).

Venting Steam: The Largest Energy Loss in Steam Systems

The optimal steam balance system ensures that the end users (steam processes) can achieve the correct volume of energy at the correct steam pressure/temperature with the required steam quality.

The optimal steam balance system ensures that the end users (steam processes) can achieve the correct volume of energy at the correct steam pressure/temperature with the required steam quality.

Flash Steam Vented to the Atmosphere. A typical steam system will incorporate an atmospheric condensate receiver that allows the flash steam to vent to the atmosphere. There are systems such as modulating process steam systems where the condensate system needs to operate at zero pressure; therefore, the flash steam is required to be consumed or vented. Unfortunately, a large number of plants vent the flash, which is a substantial energy loss (table 2).

Venting Steam: The Largest Energy Loss in Steam Systems

As table 3 shows, a small amount of flash steam being vented to the atmosphere has a significant energy loss ($26,220 per year).

Venting Steam: The Largest Energy Loss in Steam Systems

Blowthrough Steam. Blowthrough steam is generated in two primary ways. Process blowthrough steam is required for a limited number of processes to ensure proper condensate drainage. However, bypass valves around components that allow steam to freely flow into the condensate header — largely as the result of steam trap station failures — are totally unacceptable for steam system operations.

Venting Steam: The Largest Energy Loss in Steam Systems

The lack of a proactive steam trap station management program allows failed steam traps to leak or blow steam into the condensate header.

The lack of a proactive steam trap station management program allows failed steam traps to leak or blow steam into the condensate header. Eventually, this steam has to be vented to the atmosphere at the condensate collection tank system (table 4).

Venting Steam: The Largest Energy Loss in Steam Systems

All of these items are easily correctable.

Unbalanced Steam Header Pressure. Steam header balancing can be a struggle, given that process steam demands frequently change to meet production requirements.

Venting Steam: The Largest Energy Loss in Steam Systems

The only acceptable steam venting from a steam system operation is the deaerator venting noncondensable gases along with a small percentage of steam.

Unbalanced header pressure can be caused by instantaneous process changes, steam turbine operation and uncontrolled pressure-reduction stations.

Unfortunately, an easy way to stabilize the steam header pressures is to vent steam to the atmosphere to reduce or eliminate overpressurized operations (table 5).

Venting Steam: The Largest Energy Loss in Steam Systems

Deaerator Noncondensable Vent. In a steam deaerator, steam serves as the scrubbing agent to reduce the partial pressures of the gases being removed.

With the scrubbing action occurring, the deaerator must vent the noncondensable gases to the atmosphere. The only acceptable steam venting from a steam system operation is the deaerator venting noncondensable gases along with a very small percentage of steam.

Venting Steam: The Largest Energy Loss in Steam Systems

Many plants have accomplished the goal of not venting steam, and they have been rewarded with a high steam system thermal-cycle efficiency.

With the high cost of steam today, the deaerator vent must be investigated to ensure that excessive steam venting does not occur. All deaerators need to have dissolved oxygen testing conducted at least every three months, and noncondensable venting must be adjusted accordingly to achieve maximum performance.

Venting Steam: The Largest Energy Loss in Steam Systems

In conclusion, tomorrow would be a good day to start following the road map to prevent any steam from venting to the atmosphere.

 

[ Page 1 of 5 ]       

Notice