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.