Replacement of the mechanical parts of the jet base of the biomass boiler

Within the framework of the ecologicalization of ČEZ thermal power plants, a.s. (especially the reduction of SO2 emissions), in the 1990s, it was also decided to reconstruct the Hodonín power plant. During the complete reconstruction and modernization, two new identical boilers with an atmospheric circulating layer of 170 t / h with follow-up devices were installed. Fluid boiler (FK) 1 was commissioned in October 1997 and flue gas boiler 2 in September 1997. After a fifteen-year operation of the boilers, a general boiler repair was carried out, which was carried out on FK1 (brown coal) in 2012 and this year an exchange will take place on FK2 (biomass combustion).

The decisive part of the general repair was the exchange of linings on both boilers which was realized by Ditherm Praha a.s. The replacement of the bottom lining also included the replacement of the machine part of its own jet bottom, which included a sheet metal floor with welded nozzles and 20 pieces of steel hoses to connect the nozzles before entering the ash delivery into the ash coolers. The machine part was realized by ENGO servis s.r.o.

The company has already carried out a fluid bed repair, but only in a limited area of heavily damaged refractory layers on another boiler within ČEZ, a.s. The complete jet bottom exchange had not yet been performed on a fluid boiler in the Czech Republic, and therefore the necessary experience was not available.

In Hodonín, the floor was changed due to the time-consuming installation of the individual nozzles on the existing sheet metal floor, and therefore it was decided to shop manufacture a new floor. When comparing the state of the bottom to the general repair, it can be clearly stated that the bottom in FK2 (biomass) was in better condition than in FK1.

For the boilers in Hodonín, there was no horizontal bottom or the sloping walls of the lower part of the combustion chamber, which simplifies dismantling. From the present state of the project, the advantage was mainly due to Ditherm’s self-dismantling of the bottom dies, as it was not necessary to avoid strictly interfering with the metal substructure of the bottom in the event of a pressure unit.

The operator had only a drawing with the location of the nozzles (a so-called “pig tail” or corkscrew), indicating adjustments of about 1/2 of the total number of nozzles from commissioning time (blanking or reduction of the dimension by the insert) and the project drawings of the air chamber under the nozzle bottom. With respect to the investor’s request to comply with the original design of the bottom of the run-up, no change was made to the original layout and nozzle design. The nozzles are positioned according to the boiler company’s own know-how and, according to the investor’s requirement, they were installed according to the original design solution of the boiler manufacturer.

ENGO servis developed complete design documentation, including the mounting procedure, which, after approval by the developer, established the production documentation. Careful preparation resulted in minimal changes in the actual execution of the documentation. The production was carried out without any problems in accordance with the prepared Inspection and Testing Plan in a very short time.

Subdivision of the bottom of the total dimensions of 9700 × 3900 mm into various widths of 6 pieces was based on the existing division of the supporting beams, and subsequently proved to be fully satisfactory during the assembly. After drilling the axes of each row of nozzles, a drilling operation of the nozzle holes was performed in the individual parts of the plates. With respect to the investor’s requirement to comply with the original radius of nozzle bends, we did not find a Czech manufacturer that would be able to keep the original radius of bends, so we had to obtain these nozzles from DIN 1.4541 with a foreign manufacturer, in a total of 3075 pieces per boiler. This was followed by the “welding” of the inserts into the middle of the nozzles and the welding of the nozzles fitted in a transverse pitch with a difference of 50 mm between the end nozzles.

Already at the project stage, it was necessary to solve at the same time the assembly procedure, which would allow transport of new parts to the working zone with respect to the existing equipment, minimize the time of handling the parts and ensure functional handling. In the case of dismantling, it was important to co-ordinate the timing of the activities with the general lining supplier, Ditherm a.s. Prague. Self-assembly within 9 days (FK1) resp. 8 days (FK2) was then in a confined space, it was difficult to transport the individual parts to the position, while simultaneously overcoming the height difference between the transport trolley in the boiler room and the bottom of the combustion chamber.

The individual parts of the bottom were welded to the assembly and, in the place of the dividing planes, individual nozzles.

CONCLUSION

Since its inception, ENGO has carried out dozens of orders in the Hodonín heating plant. We have chosen the most important ones:

Study: Possibility to increase FK output to 190 t / h

Implementation contract (hereinafter referred to as RZ): The interconnection pipeline between blocks 3 and 4

Study: Change of biomass combustion devices

RZ: Replacement of screw conveyors on the LP outlet

Conversion of the steam outlet temperature and reclassification of the boiler passport

Study: Small non-circulating fan FK RZ: Pressure pump

Study: Combustion of biomass on CFB RZ boiler: Acoustic cleaning on FK1 and FK2

Study: Possibilities of protecting existing RPU from re-burning

Study: Removing causes of failure of superheater No. 1 in 2nd stroke FK1 and FK2

Study: avoiding sticking on FK2

Study: Mechanical cleaning of tube heating surfaces in 2nd stroke FK1 and FK2

RZ: Changing the jet bottom of the combustion chamber

FK1 and FK2

RZ: Optimization of CHLP, incl. evaluation of the FU1 ČU combustion test

From the list of selected orders, it is obvious that ENGO servis also deals with the application of biomass (hereinafter BM) for combustion in heating boilers and systems of acoustic cleaning of heating pipes of heating boiler surfaces. In addition to repeated pre-production stages (studies, tender documentation, implementation of projects), ENGO servis has carried out projects in ŠKO-ENERGO (storage, intermediate storage and transport of pellets to K80 and K90 boilers - 2006), ČEZ, a.s. - Dvůr Králové heating plant (transition of K1 and K2 grate boilers to 100 % biomass burning, 2009) and ČEZ, a.s. - Poříčí heating plant (transition to 100 % biomass combustion of the K7 boiler, including the reception object and transport into the service tank, 2012). Another segment of supply is the acoustic cleaning system of heating surfaces.

At present, the company realizes the supply of retractable expanders, expanders of operating condensates, and acoustic emission systems for leakage diagnostics of the three-unit boiler constructions “Comprehensive renovation of the Prunéřov II power plant” for the Vítkovice Power Engineering (VPE) contractor. For the same construction, we also provide a comprehensive supply of regulations and boiler commissioning by our own staff. The same scope was implemented for the VPE within the “KO ETU II” construction for four blocks.

Ing. Milan Kolovrat, Company Representative,

ENGO servis s.r.o.