HRSG Gas Side Dry Ice Cleaning
SCOPE OF THE CLEANING WORK
Eco-Genics recently competed and won the tender to provide Dry Ice Cleaning services to a major UK Power Generation Company. The scope of the work was very detailed and the controls measures were stringent.
We are proud to announce that upon completion Eco-Genics are the only company in the UK with any track record of this sort of Dry Ice Cleaning achievement which has been acclaimed from around the world with many of our competitors determined to know the method on how to clean a HRSG successfully.
The general introduction for the scope of works was as follows;
The Heat Recovery Steam Generator (HRSG) installed at the Power Station had experienced high back-pressure in the Gas Path across the module banks. This has been largely attributed to the build up of sulphur and insulation deposits in certain module banks of tubes. The HRSG has now been operated for over ten years and is now showing significant signs of iron oxide (corrosion) on the internal surfaces, which is adversly affecting heat transfer and overall performance.
It was the responsibility of the contractor to use there expert opinion to determine the full extent of the works required to meet the requirements of the client. The objective for Eco-Genics was to meet the completion guarantees, technical operational requirements of the job specification, together with achieving the most cost effective offer in terms of capital operational costs.
POWER STATION PLANT DESCRIPTION
The Power Station is a 400MW installed capacity CCGT located on the south coast of England and commenced commercial operation in 2001. The station is fueled by natural gas piped through an underground pipeline from an external supply, to the site. The site is located close to the shore adjacent to other industrial units. The nearest residential properties are across the harbour.
The station primarily includes a Combined Cycle with Gas Turbine plant with one 250MW (electrical output) ABB GT26 Gas Turbine. The combustion gases from the gas turbine are passed through a three pressure stage HRSG built by Stork Energy which drives a 150MW steam turbine with HP, IP and LP stages. The power train consist of the gas turbine, generator, clutch and steam turbine (lined in this sequence).
HEAT RECOVERY STEAM GENERATOR SYSTEM DESCRIPTION
The HRSG forms a major component of the station power train, transferring heat energy taken from the gas turbine (GT) exhaust gasses into heat energy in the form of steam These GT exhaust gasses enter the HRSG at around 608 degrees Centigrade passing through the full set of tube bundles before exhausting the HRSG stack at around 120 degrees centigrade. The de-mineralised water within the tube bundles is heated by the GT exhaust gasses to produce steam and this in the turn piped to the HP, IP and LP steam turbines to produce motive power for electrical generation.
The HRSG tube banks are vertically hung in the horizontal exhaust gas flow and are based around three classifications; High Pressure (HP), Intermediate Pressure (IP) & Low Pressure (LP). Within the HP system the steam leaving the Power Stations HRSG is super-heated and in the region of 568 degrees centigrade at 117 bar, the IP steam to the steam turbine is 568 degrees centigrade at 28bar and the LP steam to the steam turbine is 240 degrees centigrade at 4.5bar.
The HRSG is classified into 6 module banks numbered from hottest to coldest ends (i.e. closest bank to the GT exhaust is module 1) with each bank being 5 headers wide (designated A-E). Each module bank consists of tubes mainly made of carbon steel with diameter 38mm and wall thickness 2.6-3.7mm structural steel work around the banks to support them and gas guiding slide wall doors and corrugated paltes at both ends of each module bank. Tie bars are also present between the module banks, as are 2 trusses systems that anchor the banks of tubes to the HRSG Structure/casing (located downstream of module banks 2 and 4).
The approxiamate internal dimensions of the flue gas side of the HRSG are; height 19280mm x Width 11350mm and length 15000mm; this equates to a volume of 3238m cubed. The depth of tubes within a module bank ranges between 8 and 11 rows of tubes for module banks 3-6 inclusive.
DRY ICE CLEANING SPECIFICATIONS AND CHALLENGES
The specification whilst was intended to indicate the general extent of the works involved but were not necessarily exhaustive, in so far as the detailed item or associated work was concerned, it was however set out in such a way the the contractor was responsible to comply with the clients requirements. The scope of supply and special requirements meant that we had to show due diligence and come up with a safe, efficient and effective solution to complete the HRSG Gas Side Clean as per the clients requirements.
This cleaning procedure was a very difficult job to plan, the timescales of the job were fixed and the level of debris accumulation was always a concern especially with the depths of the module banks. As a fore mentioned the client made us aware that they had not had any experience or knowledge of the exact cleaning procedure to follow so the complete sequence of work was determined by Eco-Genics.
Banks 3-6 had to be deep cleaned removing all deposits from in between the fin bank tubes of the HRSG. Eco-Genics HRSG cleaning experience to this point was nil like every other UK dry ice cleaning company, however we were able to provide a procedure and manufacture specialised spreading tools that made it possible for us to achieve the clean to the clients requirements.
Eco-Genics are now the only company in the UK with any track record of this sort of clean and the achievement has been acclaimed from around the world with many of our competitors determined to know the method to clean an HRSG successfully.
After winning the tender Eco-Genics window of opportunity to achieve there requirements was just 28days. Eco-Genics were able to surpass the requirements and brought the HRSG Dry Ice Gas Side Clean in a full 7 days ahead of schedule leaving each module bank free of all deposits. The Eco-Genics team even cleaned all the historical debris accumulation from the bottom dead space with over 7 tons of debris removed. Not to mention the the project was completed safely and was on budget.
Congratulations to our client and to my team members for a job well done.