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View looking up in the chimney (Unit 2 stack on left) starting be be lowered

As most of you know, I have just finished an outage where the #2 steam boiler and steam turbine / generator were overhauled. During this outage I was tasked with the change out of the stack liner (which is the metal tube inside of the concrete chimney), replacing the scrubber tower outlet dampers, lining the scrubber outlet ducts (before the dampers) with an inconell alloy called Hastelloy and given the ASTM designation of C-276. It is a nickel alloy and is very resistant to chemical attack. The chimney is 385 feet tall with the stack liners sticking up an extra 15 feet or 400 feet above the ground. The liners are 16 foot 7 inches in diameter and are 360 foot tall (they start 40 feet up in the chimney)

The flue gas contains sulfur. In the scrubbers the sulfur is taken out of the flue gas and removed in a slurry. This mixing with limestone and water forms calcium carbonate to precipitate out, but makes the flue gas very wet. The moisture from the water is carried over out of the scrubbers and into the flue gas. This makes the flue stream contaminated with sulfuric acid. This acid eats the carbon or stainless steels that make up the duct work, dampers, and stack.

Unit #2 jacking system to lower liner

ST#2 lifted off the support steel (elevation 90 feet above concrete) the stack stretched about 3/4" when put in tension vs compression (notice the chalk mark from when it was on the steel)

Unit 2 stack on the ground and the floor being cut out of it.

Coatings have been applied to the metals of the duct work system, but these coatings are a temporary solution and every outage (every two years) they have to be hydro blasted off (with 40,000 psi water) and the re-applied. This cleaning and re-application process not only takes lots of time, but also costs lots of money. These two (mirror image) boilers were built in the mid 1970's and have two scrubber towers each. The purpose of the two scrubber towers is to be able to use one with one out of service and maintenance can be performed. When the EPA made some additional pollution control rulings in 2001 these scrubbers have to both be operated all the time to remove enough sulfur. This additional tower makes the flue gas cooler and wetter, thus more acid attacking the steel.

Liner being cut apart for removal.

Scaffolding erected to re-assemble the new stack liner

The chimney contains two stacks (one for unit 2 and one for unit 3). The stack was removed by placing hydraulic jacks on the chimney roof, and then running some steel jacking rods down the liner and attaching the rods onto some lifting lugs (seen here). Then the jacks lift the rods off of stop blocks and lower them the 20 inch stroke of the jack to another stop block. This process is repeated over and over until the heights are reached. The stack was lowered down the chimney until it was inches above the floor. Then 10 feet were cut off and the newly cut can was cut into thirds to get out of the chimney.

Here is a veiw looking down the chimney at the lowering of the ST2 stack liner.

Here is a view looking up with the #2 stack liner missing. You will notice the newly constructed #3 stack liner still in place.

The new stack was assembled in the opposite fashion. The new stack was brought in in thirds and then assembled on an assembly cart. This cart was then rolled into position under the liner and welded to it. The new stack was made from a high strength carbon steel (A-588) with a 1/16th inch wall paper of hastelloy (C-276) on the inside. Then once the carbon steel was welded together a 6" wide strip of hastelloy was welded over the joint giving a complete hastelloy interior of the new stack. Once the stack was assembled and put together, it was then raised into place in the same fashion that it was removed.   Here is a view looking up with the #2 stack liner missing. You will notice the newly constructed #3 stack liner still in place.

New liner with insulation on the exterior (almost back into position)

Duct work coming out (this is the converging tee)

Vertical section of duct work to be replaced

The new stack liner was then insulated with a 2 inch fiberglass insulation to minimize the flue gas from cooling off to the point where it condenses any more water prior to exiting the stack. In addition to the stack liner replacement, we replaced some of the duct work. Here is the duct work being removed and then re-installed. Once the duct work went back in, the dampers were placed and then the interior of the horizontal ducts adjacent to the dampers were also lined with C-276 Hastelloy.

New duct work being lifted back into position (notice the new dampers on the ground)

Completed duct work ready for service (with new dampers and seal air fans)

Even though this was not my project, it did make for some interesting photos. Every once in a while I would walk across the turbine deck and get a photo or to. Here is the turbine housing coming apart. This is the low pressure turbine (this turbine has a High pressure 2,400psi turbine, an intermediate pressure 1,200 psi turbine and a low pressure 600 psi turbine). This is the low pressure housing coming off. If you look to the right you will see the intermediate and high pressure turbine blades already exposed.

Turbine disassembly

Looking into diaphragms (stationary vanes) where turbine sits.

Turbine shaft out for inspections (low pressure turbine on the left).

Disassembly of Generator

Re-assembly of rotor back into stator

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