This is an informative interview with Yefim Kashler, Oil & Gas Executive, PE Performance/Gas Turbine Engineer, NYPA and Bobbi Monacelli, Co-Owner UDSCleanblast.com and Indoor Air Quality Care (HRSG Maintenance and Cleaning Company)
Bobbi – HRSG’s accumulate contaminants and deposits on their finned tubes, which are used to conduct heat. Even in small amounts, the contamination resists the transfer of heat through the fins, resulting in a loss of efficiency. If the contamination accumulates to a certain amount, plugging airflow, it may severely restrict the flow of gas across the tube banks, which is an important part of the process. When there is a case of severe blockage the control unit senses back pressure does this slow the turbine?
Yefim – It doesn’t slow the turbine, the turbine runs at constant speed. What happens is it creates elevated back pressure on the turbine. Because of that the turbine generates less power, the turbine efficiency drops, and the Heat Rate (amount of energy used to generate one kilowatt-hour) becomes higher as well.
Bobbi- Explain why dry ice blasting is the process the NYPA uses for cleaning HRSGs?
Yefim – Pressure washing is not the answer because it creates highly corrosive waste stream with ammonia-sulfur compounds. That creates environmental problems with disposal of that waste. This corrosive liquid can also corrode the tubes, the fins and the entire boiler structure. With the dry ice you blast it off and it never becomes wet and corrosive, which is the best answer to this need.
How do you measure the airflow and back pressure across the HRSGs?
Yefim- We have instrumentation that records it. The backpressure went from 21” WC (water column) before to 18”WC after the cleaning. As mentioned before, the lower the backpressure, the better the turbine output, the higher the efficiency and the lower the Heat Rate.
Bobbi- How do calculate the cost savings?
Yefim- There are 2 folds here. The manufacturer of the gas turbine has curves that allow you to determine the production and efficiency losses at elevated backpressure. The second part is that there is also a manufacturer’s limit on how high the backpressure can go before the equipment would suffer a catastrophic damage. The control system would automatically shut down the turbine if that limit is reached. If the boiler deposits are high enough to approach that backpressure limit, in order to prevent the automatic “turbine trip” the operators would reduce the power output to stay within the allowable limits. In our case, we had to reduce the output by as much as 20-25 MW (Megawatts). So you are losing a significant amount of power, corresponding revenue and efficiency.
Bobbi-How often should the HRSG be cleaned?
Yefim- It depends on sulfur content in fuel and other factors. If Sulfur content is high it will clog up your boiler surfaces quicker. If the water make up to the boiler is cold, it would also allow more deposits on the boiler tubes. If you operate on natural gas and your water temperature is relatively high you’re not going to create too much deposits. Deposits are mostly formed on colder sections of the boiler, but sometimes, depending on the process, may form on hotter sections. So, depending on your process, the cleaning should be performed anywhere between 1 and 8 years.
Bobbi- As an engineer, what else in your facility do you feel would be great to clean with ice blasting?
Yefim- There was ice blasting opportunities for paint removal, turbine cleaning, generator cleaning, etc..
Bobbi- Our company does walnut shell blasting, steel shot, baking soda, all media blasting, surface preparation for painting
Bobbi-There is a controversy over the tube spreader process, that they get better numbers,
Did we achieve numbers you were hoping for?
Yefim- Your company and the ice blasting exceeded my expectations. I was quite surprised by the degree of improvement. In my previous experience the improvements were not that pronounced.
Bobbi-How did our safety record help you in the decision making of choosing us?
Yefim- You crew and company did great. You were very qualified. You were professional with your clearing your crews with our safety and security. You didn’t delay in any way our outage schedule. Everything went smoothly.
Advanced Indoor Air Quality Care
3 Kadel Drive
Mount Arlington NJ, 07856