Comprehensive rehabilitation of ETU II

Comprehensive rehabilitation of EPR II

A comprehensive rehabilitation project for the EPR II electric power plant consisted (among others) of a complete replacement of the equipment in the boiler room for three blocks. Working as a subcontractor for its partners IVITAS, a.s. and Vitkovice power engineering, MORE delivered a basic design of firing system for lignite-fired boilers in accordance with the written parameters it was given. In 2016, the realization of all three blocks finalized and guarantee tests were performed, which confirmed the success of the project.

Production block parameters

• Block rated capacity: 250 MW_e
• Controled power range: 50 – 105%
• Minimum boiler power without use of stabilization burners 45%
• Main fuel - Czech brown coal with LHV (NCV) ranging from 8.5MJ/kg to 11MJ/kg, moisture content (raw) 31% - 34%, ash content (raw) 35% - 46%

Boiler parameters

• Flow rate of superheated steam: 660.4 t/h
• Maximum flow rate of superheated steam: 669.4 t/h
• Pressure of superheated steam: 18.26 MPa
• Temperature of superheated steam: 575 °C
• Pressure of reheated steam: 3.65 MPa
• Temperature of reheated steam: 580 °C
• Temperature of supply water: 251 °C
• Performance range without stabilization and complying with the specific parameters: 50 – 105 %
• NOx emission limit 200 mg/m3 (standard conditions and reference content O2 6%), utilizing the primary measures to reduce NOx emissions
• CO emission limit 250 mg/m3 (ref. conditions)

Our responsibility in the project

Our task was to propose a boiler and firing system design and create a foundation for the basic design, including:

• A design of the geometric arrangement of the furnace
• A plan of the primary measures to reduce the NOx production and zoning of the air and fuel
• A design of the combustion mode to fulfil the requirements of the guaranteed parameters within the entire range of performance and operation without slagging
• Testing the concept of the combustion chamber, combustion design, and denitrification with the help of the CFD method
• Creation of the technical concept for the supply of mills and pulverized coal classifiers
• Design a new solution for the classifier of the pulverized coal and testing the concept with the help of the CFD method
• A design of pulverized coal pipes and pulverized coal burners
• A design of flue gas and air tracks of the boiler, including fans
• A design of the tract for flue gas recirculation, including a fan
• Development of the specifications for the field instrumentation of the MaR system for beater wheel mill circuits, including the flue gas and air tract of the boiler
• A project of the algorithms for beater wheel mill circuit operation, air mode and flue gas recirculation
• A design of the system to reduce unburned residues of cinder by flue gas recirculation in the slag heap, testing of the concept with the help of the CFD method
• An analysis of unsteady and emergency conditions of the boiler and proposed measures
• A design of the system to monitor combustion stability, a project of algorithms and installation into the control system
• Creation of the specifications for related professions
• Setting and optimization of the boiler combustion modes

We applied our know-how gained over the years and managed to decrease emissions of  NO_x below the limit of 200 mg/m³ under reference conditions without using secondary measures for NO_x reduction.  To achieve this result was not an easy task, and is therefore greatly valued by us as professionals.

CFD Analysis of an FGD Absorber

A customer using an absorber for desulfurization of flue gas was trying to solve the problem of sediment on the wall of the absorber, which made the equipment parameters worse during the desulfurization process. A CFD analysis was applied on the current operational condition of the absorber in order to identify the causes of the sediment on the walls and in order to find solutions and modifications that – according to analysis results – lead to suppression of sediment creation and to better diffusion of suspension in the space of the absorber.

The aim of the analysis was to identify possible causes of the sediment (made of solid suspension particles) on the walls of the absorber. The calculations also concentrated on the way the suspension was sprayed, its effect on covering the cross-section of the absorber and possible impact on the efficiency of desulfurization. Moreover, the changes of geometry of inlet guide vanes were calculated with respect to the more intensive swirl of flue gas in the space of the absorber. The analysis included calculations of the current conditions under various operational circumstances, calculations of various modifications of the flue gas outlet and atomizer jets under various operational conditions of the absorber.

The CFD analysis proved that there was a reverse swirl and an increase in the local dampness of the walls, which contributed to sediment on the walls. It showed the influence of speed and potency of droplet streams in the atomizer on the flow and distribution of dampness in the absorber. Thanks to the CFD analysis, necessary modifications of the atomizer and internals took place to improve the working conditions of the absorber.

Some visualizations

Places with higher risk of on wall fouling

Velocity vectors, visualization of vortices close to the wall (before changes)

The radial velocity at the wall of the absorber, visualization of transport speeds deteriorating deposits (before changes)

Mass fraction of moisture on the walls of the absorber (before changes)

Mass fraction of moisture on the walls of the absorber (after change, 24 nozzles in atomizer)

 Effect of changes in the number of nozzles on the temperature field

The temperature field in the absorber (32 nozzles in atomizer)

The temperature field in the absorber (24 nozzles in atomizer)

Realization

After checking the impact of the changes in design, the customer used the findings of the CFD analysis and documentation to carry out modifications and achieved an improvement in the operation of his equipment.

Making the operation of an EPR-I Boiler Room environmentally friendly

Between 1996 and 2010, we carried out projects for our customer Prunerov-I Power Plant in CEZ Group for making their operations more environmentally friendly.  These activities have led to a reduction of NOx emissions, improvement of boiler performance and fixing problems that were caused by old technology or by a gradual change of their fuel base. The projects are briefly listed below. In addition to this list, our company performs services including long-distance diagnostics of 350t/h-boiler operations, on-site measurements and setting of the combustion mode.

Individual realizations

•  1996 – A plan of primary measures and a design of operational algorithms to reduce NOx emissions in the K3 pulverized coal-fired boiler as a subcontractor for Vítkovice a. s., including operation optimization, emission NOx rate: 250 - 350 mg/mN3
• 1997 – A plan of primary measures and a design of operational algorithms to reduce NOx emissions in the K5 pulverized coal-fired boiler, as a subcontractor for Vítkovice a. s., including operation optimization, emission NOx rate: 250 - 350 mg/mN3
• 1997 - Modelling and a design of modifications of the classifiers of the beater wheel mills for the K3-K6 boilers and subsequent realization of these modifications within the increase in performance reserve of the mills
• 2000-2001 – Model testing of the designs modifications of pulverized coal pipes, burners and combustion chamber (combustion) of the 350 t/h boilers to solve problems with abrasion and slagging in the combustion room
• 2004 – Measurement of the Prunerov I Power Plant beater wheel mill circuits to identify the impact of return dampers on a lower-consumption mode and boilers
• 2003-2004 – Realization of an online system of operational system prognosis and beater wheel mill circuit reserves for the 350 t/h boilers
• 2005 – A plan of modifications to reduce NOx emissions below 250 mg/m3 in K5 lignite pulverized coal-fired boiler. Realization by Vitkovice Heavy Machinery, a.s.
• 2006 – Coordination and monitoring of combustion stability and a low-calorific fuel combustion test
• 2007-2008 – Proposed measures, modifications and realization for K3, K4, K5 and K6 boilers in order to increase efficiency by reducing the ratio of slag that has a high rate of unburned residue in the discharge
• 2010 – Modelling of abrasions on the ECO input element, assessment of the efficiency of protective internals, new proposed measures against abrasions
• 2010 – An analysis of possible causes for the larger amount of combustible matter in the fly-ash of 350 t/h boilers

Eliminating critical errors by optimizing equipment

The operator of a lignite electric power plant boiler that has 4 x 200 MWe blocks went through frequent blackouts due to one of the blocks exceeding the amperage of its axial ID fans. The emergency shutdowns of the ID fan led to a shutdown of the entire block, which meant interruption of electric power production in the block. The cause of the blackouts was not completely identified at the beginning. One of the parts that was diagnosed, and remained short-listed as a cause, proved to be the reason for the blackouts later on. It was a common flue gas pipe which served as an outlet for the axial ID fans’ output. This case was typical unwanted Single Point Of Failure (SPOF), which was eliminated by use of Computational Fluid Dynamics (CFD) both for finding and proving the cause and for finding the optimized design.

Analyzed flue gas pipe

The joint pipe for two fans (ID) was analyzed by CFD of internal flow in the pipe. It calculated the data concerning pressure and speed in the pipe, of which the values and shape are shown, in the original (failing) state, alternative and final optimized state. The original and final optimized states are shown below.

Identifying the source of the problem

The identified source of the problem was an unsuitable outlet of air displacement into a shared exit which led to a complex flow and “tear away” of air currents.  The left branch was forced to work with a double pressure loss, which led to a transfer of power to the right fan and caused it to shutdown (overloading). The source of the problem was identified and fixed by a simple modification.

Return on investment

The costs of this optimization were quite insignificant in comparison with the operational losses and, consequently, partial devaluation of investment costs of the original equipment caused by the emergency blackouts. Moreover, proper optimization helped to fast renew the quality of the design and the realization of the optimized unit, as well as completely fixing the cause of the problems. CFD was able to find the source of the problem, test more options on how to fix it, and help choose the optimal options for realization.

Visualization

Pressure drop (Pa) comparison of left (magenta) and right intakes (beige) into joint pipe for two states of design, failing on the left side and optimized on the right side of graph.

Shape of joint pipe, in lower part are located two intakes (connecting outlets of axial ID fans). Colour grid with 1 meter step.

Visualization of total pressure in the critical part of joint pipe. Upper is failing design, lower is optimized design.

Visualization of velocity vectors in the critical part of joint pipe. Upper is failing design, lower is optimized design.