Four large flues. Four boiler outages. How to install PennguardTM linings for 20 years of service with minimal maintenance
CLP Power decided to install PennguardTM linings in the Castle Peak B chimney flues and to do so within scheduled outage time only. More than just being quick, the installation would also have to be safe and the quality of the work would have to result in a lining service life exceeding 20 years, without any significant maintenance or repair.
The CLP Power project team made a key decision to perform the lining work during the relatively long, scheduled boiler outages, rather than the shorter FGD tie-in outages. As a result, each of the PennguardTM lined flues would be exposed to several months of high temperature, non-FGD service. This is acceptable for PennguardTM linings, provided that any external insulation is first removed from the steel flues.
CLP Power awarded the lining installation contract to Balanced Engineering & Construction Pte Ltd (“BEC”) from Singapore. To ensure a safe, timely, high quality completion of the works, BEC paid close attention to several key aspects of the project.
1 – Safety
For the duration of the project, a designated Safety Manager was part of the BEC team on site. The Safety Manager worked with a small team of assistants, who were tasked exclusively with enforcing safety rules at all times. Furthermore, any persons entering the chimney were strictly required to have completed both Hong Kong Government and CLP Power safety courses.
2 – Access and weather protection
A strong platform, with a full floor and a fast, separate hoist for materials supply was built, to ensure optimum access to all steel surfaces, as well as an uninterrupted supply of PennguardTM materials to the installation crews. To protect the works from the torrential rains that can sometimes hit Hong Kong, the top of each flue was closed off with a temporary waterproof seal.
3 – Surface preparation
When preparing a steel flue for a PennguardTM lining installation, the substrate needs to be grit blasted to an SA 2 1/2 “near white metal” cleanliness with a minimum 35 µm surface profile. BEC prepared for this by installing a single, 336 m³/hour compressor on ground level, with 3 blast pots placed on the support floors within the chimney windshield.
PennguardTM linings offer a great advantage for lining used steel flues that were not originally fabricated as “fit-for-lining”: small imperfections in welds, such as ripples, protrusions and pinholes can be left uncorrected and even slight pitting in the steel plate is not a problem. Surface preparation and spray application of PennguardTM Block Primer could be completed in 27-31 days in each of the flues.
4 – PennguardTM lining installation
The PennguardTM installation work was performed by two teams, each with 8 trained brick layers, working in two shifts per day. Lining installation in two of the flues was completed in less than 24 days, while two other flues required longer, 34 and 36 days respectively.
5 – Quality Assurance
Hadek was present on site at all times during the work. One Hadek QA Inspector attended surface preparation. During installation of the PennguardTM lining, one Hadek QA Inspector was present during the day shift and a second Hadek inspector worked during the night shift. As on most PennguardTM lining projects, Hadek performed intensive, systematic QA supervision, allowing any defects to be identified and corrected immediately.
Cold spots: a fundamental problem for steel chimneys and chimney flues eliminated by the use of PennguardTM linings
For structural stability as well as for construction purposes, every steel chimney flue (or steel chimney) has stiffeners on its outside. In these areas, the steel is much thicker than the standard plate thickness and it is often difficult to apply an effective thermal insulation.
As a result, these stiffeners generate “cold spots” on the inside of the chimney flue, where excessive condensate formation can take place especially during start-ups and low load operation (Figure 1).
The use of thermally insulating PennguardTM linings on the inside of steel flues eliminates this problem. As shown by Figure 2, the PennguardTM lining system will provide effective thermal insulation in all areas of the flue, even where the outside flue surface is covered with external stiffeners.
In newly constructed chimneys, PennguardTM lined steel flues do not receive any external insulation. When a PennguardTM lining is installed in existing steel flues, it is usually necessary to remove any thermal insulation system present on the outside flue surface. In the case of the Castle Peak B chimney flues, a glass wool thermal insulation had to be removed prior to commissioning the lined flues.