Precision Iceblast Corporation was hired to perform conventional dry ice blasting and deep cleaning of four Heat Recovery Steam Generator modules inside one Vogt/Kawasaki HRSG at a Combined Cycle Power Station in Penang, Malaysia. These four modules are composed of eight faces. Each face is approximately (24 ft wide x 62 ft tall). The largest module was made up of 13 tubes deep while the smallest module was made up of eight tubes deep. Work took place over a 15-day period of an 18 day outage. PIC provided highly trained and experienced personnel for ice blasting and the deep cleaning process along with the required equipment to perform this work scope. Resources used in the process were two high-pressure blasting guns (PIC 56XD’s), a high-pressure compressor, and four crew members (one supervisor, one hole watch, and two blasters) per shift. Remaco provided the compressor, diesel fuel, dry ice pellets, and access into the unit via scaffolding.
Upon pre-inspection of the HRSG, it was discovered that there were extremely large amounts of insulation blocking the airflow throughout the first 3 modules. It almost appeared as though someone tried to clean the bundles at a prior time and packed the insulation further into the bundles, as it was very hard packed in the middle. A bore scope inspection showed the insulation was as far back as 6 tubes deep in these modules. The last module, faces 7 and 8 specifically, were primarily plugged with rust. The scaffolding was built to PIC specifications and would not pose any hindrance on the work. All other equipment was on hand for staging upon PIC’s arrival to the station. The only exception was an aftercooler and air dryer. There was one available, but they were not large enough to handle the high bars of pressure we require for our cleaning process. Therefore, we made some modifications to our equipment to make it work and complete the job to expectations and within the given time frame.
On face #1 we discovered two tube ties that were broke loose that will need to be repaired. The unit’s HP Superheater tubes were in very good shape and only had insulation above the second tube tie. However, it was starting to pack in the module after the first three tubes deep and increased from there. All faces and modules had insulation present. Most faces were plugged on the upper 2/3 of the face and module. This is a major contributor to high back pressure issues by restricting or even eliminating air flow through the HRSG and also affecting the heat transfer within the HRSG. In the last module, we observed primarily rust deposits. This also contributes to a loss in airflow and heat transfer.
Starting on face #3 and going forward, we had to change the way we were blasting and deep cleaning. The insulation was so packed that we had to change the direction and nozzle placement in order to remove the insulation. The normal sequence of deep cleaning was also adjusted to effectively get the front and back of every tube cleaned. The blow down wand was changed several times in order to get the correct angle on all the tubes throughout the tube bundle. This was done on every face up to the stack. Due to each bundle being just a little different in the flex of the tubes the process was evaluated every time and inspected to make sure the optimal cleaning was taking place. This included using various deep cleaning bars and wands and placement of them.
|77% reduction or approximately 10mbar.|
Approximately 3-4 Deg C reduction in stack outlet temperature.
Observed good heat transfer at Superheater 2 region by approximately 20 -30 Deg C. Higher steam temperature.
|Approximately 2-3 ton/hr increase in steam flow. Very noticeable when compared with feedwater flow.|
The cost in fuel savings alone will more than justify a regular cleaning schedule for this unit. Overall, we removed over 1KG ton of debris from the unit. The majority of the debris removed was insulation which does not weigh much, but is a major restriction inside of a HRSG.
Resources include two high-pressure blasting guns (PIC 56XD’s), one high-pressure compressor, and four laborers (one supervisor, one hole watch, one laborer and two blasters) per shift.
**Since the original cleaning back in 2016, PIC has cleaned the second unit at this power plant and this same unit again in 2019.