Dry Ice Blasting HRSGs
While our blasting rice doesn’t literally make steam, it plays a critical role in making sure steam turbines in power plants operate at peak efficiency. Dry Ice Blasting is the optimal method for cleaning a vital component of Power plant system called a HRSG (commonly referred to as a Her-sig).
What are HRSGs?
HRSG stands for Heat Recovery Steam Generator. In modern power plants, the primary generation of electricity is driven by natural gas fired turbines which produce hot exhaust gases. HRSGs recover the heat remaining in the exhaust and use it to produce steam to drive a second round of electricity generation.
HRSGs consist of building-height tubes covered with fins that maximize surface area for heat capture. As water circulates through the system, it is converted to steam. The array of tubes and steam drums is designed to carefully control heating and regulate pressures so that all the water in the system converts to the super-heated steam required to drive a steam turbine. Steam power is a simple idea from the beginning of the Industrial Era, but the engineering of HRSGs is complex. Here’s the HRSG explainer you didn’t know you needed:
Heat Recovery Steam Generator (HRSG) Explained – saVRee
Why Do HRSGs need to be cleaned?
The exhaust flowing over these tubes (Economisers, Evaporators, and Superheaters) leaves deposits and creates oxidation on their surfaces. This fouling reduces the effectiveness of the heat transfer process. Reduced efficiency at any phase of heating and evaporation causes irregular pressure throughout the system. Unchecked, stresses caused by unbalanced pressures cause component wear and even failure. Mechanical maintenance and repairs of the system requires disassembly and downtime (loss of production) leading to significant costs and lost revenue. Regular cleaning of the exterior of the tubes maintains their efficiency, reduces maintenance, and repairs, and lowers the risk of component failure.
Image from: Heat-Recovery Steam Generators – Combined Cycle Journal
Why is Dry Ice Blasting the best method for cleaning HRSG tubes?
HRSG tubes have complex surfaces and are tightly packed together to maximize the amount of steam the system can produce. Disassembling the arrays or applying chemicals to strip the contaminants are not an option, so the job must be done with the tubes in place. A cleaning system that can be delivered into tight spaces is required. Power plants have settled on dry ice blasting as the standard for this cleaning. Other industrial cleaning methods such as high-pressure water cleaning or media blasting have clear drawbacks.
Drawbacks of Cleaning HRSGS with High-pressure Water Cleaning:
- Water mixed with fouling creates an acidic environment that fosters more corrosion.
- The process produces a slurry of water and contaminants that hardens like concrete on equipment.
- The high-pressure water streams will remove insulation along with contaminants, driving it deep into the tube arrays, making fouling worse.
Drawbacks of Cleaning HRSGs with Media Blasting:
- Media blasting is an abrasive process that over time will thin out the tube walls causing leaks and damage to other components.
- Huge amounts of secondary waste is generated because both the media and the removed fouling must be cleaned.
- Wet blasters require large volumes of water to deliver the grit, unsustainably wasting water and adding to cleanup.
Dry Ice Blasting has all the advantages of high-pressure water and media blasting without the drawbacks. Dry ice pellets accelerated by compressed air instead of water can reach all the surfaces that need to be cleaned and do so without damage or secondary waste.
Advantages of Cleaning HRSGs with Dry ice Blasting:
- Dry Ice uses thermal shock to dislodge the fouling, so chemicals are not required to break down mineral salts and other complex deposits on HRSGs.
- Dry Ice is nonabrasive and will not damage the tubes or other components
- Because Dry Ice is made from CO2 that sublimates (reverts to a gas) upon contact, there is no secondary waste to clean.
- Dry Ice Cleaning is Sustainable: the process takes chemicals out of the cleaning equation and uses no water.
While we aren’t literally making steam with Dry Ice, our blasting rice plays a crucial role in maintaining HRSG’s peak performance as they deliver the power making everyday life possible. And that’s pretty cool.
