1, Site situation
ESEC located a city which winter temperature at -33 degree C and the summer time site temperature can up to 34 C, air condition system face a lot of challenge due to site temperature big change yearly.
Figure 1 summer site temperature 34.1 °C
Figure 2 Site winter time site temperature -32.3 °C
2 HVAC system installed
For the main building, HRSG building with CTG building installed two air handle unit( HUV 501 502) STG building installed two unit heater (HUV503 and 504), Auxiliary building installed two unit heater (HUV505 and 506). Demineralization building one unit heater install HUV 507
For the air handle unit, if the temperature < 4 degree C, the heating switch will close the heating burner will be on, if the air temperature is bigger than 10 degree C the heating switch will open then heat will stop. Top of the HRSG installed 14 damper to connect outside for the flush air, the 4 roof fan at HRSG to keep the air flow and pull air from top the HRSG to keep the room temperature
Plant DCS has a page created for monitory individual room temperature and alarm set up for operator to monitory
Each room installed door for air isolation, there is adjust damper to adjust room pressure between STG room and Auaxiliary boiler room . for the individual building installed air handle unit and electrical heater, ventilation fan.
3 Operation Challenge and solution
3.1 Challenge 1: – Inadequate building temperature control leading to equipment freezing during winter
Cold air come through the main building to freeze transmitter caused CT1 trip due to HRSG IP economizer flow transmitter freeze and LP and IP drum level transmitter also experienced freeze at winter time, HRSG#1 HP steam pressure freeze and cause the CTG runback.
solution: as per figure 4 for each damper to prevent the cold directly blow to sensitivity transmitter so, install a aluminum shield informant of each damper to prevent directly blow to equipment.
Figure 3 air damper louver with linkage
Figure 4 installed stainless shield to prevent air directly below to transmitter
Figure 5 Damper position check for operator at winter rounds
Figure 6 drawing is showing damper position
In the meaning time to label each damper from drawing per figure 6 then according to the different lovers air flow location to label the different Zon
The HRSG’s are now set up with wind breaks as well as all louvers are operated by a temperature controller. The controller is set up with three zones. Some damper faces the important transmitter to close early then another zone ad below:
- Zone 1 closes louvers 6,7,8,1,11,12,13,14. This zone closes at -0
- Zone 2 closes louvers 9,10,11 . This Zone closes at -5
- Zone 3 closed the remaining louvers 2,3,4,5. This Zone closes at -10
The operation on the roof fans has not changed it is still controlled with the thermostat in front of the IP drum on the south wall. If for any reason a louver is not closed in a zone on a very cold day, operators can fix this by removing the linkage and closing it manually like in the past
3.3 Challenge 2, due to Unwanted hot air flow between the main generation building and the HRSG Penthouse enclosures, -Inadequate building temperature control leading to overheating and premature equipment failures, as per figure Penthouse temperature over 55 degree C
Figure 7 Local temperature gauge shows the top of HRSG penthouse temperature
Solution:
Root cause investigated conducted by the Plant and Plant Engineering (MOC 21129325) concluded that there is no physical barrier between the systems that had been provided by two vendors when the plant was constructed. The ventilation of the main building (Gas Turbine and Steam Turbine building) was designed by KBV; whereas, the ventilation of the HRSG was designed by Vogt/MHI. The imaginary barrier between these two systems, is located in the HRSG Penthouse.
The study concluded that by installing physical barrier between these two systems, each individual system can operate as per the original design scheme for the system. The plant has also initiated a test to prove this concept. Physical and temporary barriers using scaffold and traps were installed in the penthouse on Unit2 to separate HRSG from the main building. The test results seem to prove the conclusions of the study.
The Plant had indicated that this action reduced temperature inside the penthouse by 15 degrees. However, there are no temperature points in the penthouse that are trended in PI historian. Thus, the magnitude of the change could not be confirmed.
The purpose of this project will be to install a permanent barrier between Shepard Main Building and HRSG Penthouse. The project will include addition of wireless temperature transmitters to monitor the change. The barrier will first be installed on one unit and evaluated after the installation. If the implementation will provide with the expected improvements, the solution could also be applied to the second HRSG unit.
3. 3 challenge 3: The supply air fans are pulling dust and debris into generation buildings resulting in operational issues (e.g. fouling of motor filters)
Solution: A detailed assessment of ESEC’s process area HVAC systems was conducted The following modifications to the main makeup air units are to be made:
1) Remove the internal 1/2″ mesh from Shepard’s makeup air units AHU-501/502/503/504
2) Replace the existing 1/2″ external mesh with 2″ mesh on Shepard’s makeup air units AHU-501/502/503/504
Note that a subsequent capital project is planned for 2019 at which point further improvements may be made to these systems (e.g. additional filtration for summer months)
In winter, the inlet screens at Shepard’s makeup air units will buildup ice and restrict air flow Makeup air units required to maintain certain number of air volume changes for building area classifications. Ice buildup must be removing manually which is a safety concern. The existing arrangement with internal and external screens is redundant. The internal mesh is difficult to access for removing debris.
Note that increasing the mesh size will allow more debris to enter the units. This is likely to increase cleaning frequencies and could potentially affect reliability. If the negative consequences are realized and deemed to outweigh the benefits, the inlet screens will be revisited. Other options include heat trace or mechanical methods of removing ice buildup
3.3 Challenge 4: Ducting is not directing the flow efficiently to the inverter room
The Plant has also identified high temperatures inside the Invertor room. The Invertor room is adjacent to the Battery room. The HVAC ducting is common to both rooms. The part of this project will be to modifying ducting between these two rooms.
Solution: Solution modifying the ducting between room to re-disbtution of the cooling air to allow it move evenly flow cooling air to two room, invertor room has more heating load then battery room, so more cooling air flow through
3.4 Challenge 5 low temperature at inside of Disc-cloth filter Low temperatures inside Disc-cloth filter building caused some of the instrumentation to malfunction.
Solution: it increased heater size from 7.5 kW to 15 kW.
3.5 Challenge 6: HRSG#1,2 figure racks high temperature, after installed the isolation to isolate the HRSG penthouse hot air, hot air increased the figure racks to up to 50 degree C
In addition to the above mentioned installing additional fans for cooling on the HRSG finger racks (4 total) as per figure 5 the arrow located new install cooling fan which help to Improve system efficiency and reliability
3.6 challenge 7: cooling tower electrical room over temperature in summer time:
In the summer time, cooling electrical room has lot of heating generated by the cooling VFD 14 of them, summer time VFD always operated at 100%, but the electrical pakage not install air condition device cause the room increase to over 40 degree C and it cause the VFD over heating to trip the cooling tower Fan, so in the summer time plant rented a moveable industrial air conditioner to keep the room temperature cool.
3.7 challenge 8: the 6 kV electrical room temperature low cause the DCS communication module trip lost communication between the power plant with local dispatch center, so in the winter temperature extra heater was located the room when the room temperature below the set point the extra heater will start to warm the package
4. Conclusion
Plant created Preventive maintenance work order in the Maximo work order system to check the air conditioner health before summer come and check and test all the unit heater before the cold weather season , plant prepared extra heater to help the equipment wormer, the good practice of the plant maintain the air condition system to improve the plant reliability to 99.8% of 2020 year.