Nozzle Steam Distribution with a Remote Mixing Chamber

Abstract

The experience of operating powerful energy steam turbines has clearly shown that a significant share of losses with reduced steam consumption is accounted for by the steam distribution system, which is characterized by intensive throttling of steam entering the turbine’s flow section. Of the two main steam distribution systems—throttle and nozzle—nozzle steam distribution has an obvious advantage, where, unlike throttle, a reduction in steam flow through a turbine is achieved by throttling not only the entire steam stream but only part of it in a series of consecutively opening valves. To implement this method of steam distribution, it was necessary to introduce a special regulating stage into the turbine flow section, separated from the remaining stages by a regulating stage chamber (mixing chamber) designed to equalize uneven velocity fields at the entrance to the first unregulated stage, which are especially distinct with partial turbine loads. A detailed analysis of the advantages and disadvantages of the throttle and nozzle steam distribution is given and it is indicated that, taking into account all the additional consequences associated with the use of nozzle steam distribution, its advantage over the throttle becomes noticeable only when the turbine load is reduced by more than 25%. To eliminate the disadvantages inherent in the nozzle steam distribution, it is proposed to move the mixing chamber (chamber of the control stage) outside the turbine casing, thereby eliminating the control stage and greatly simplifying the supply of steam to the high-pressure cylinder of the steam turbine. In conclusion, a constructive solution for nozzle steam distribution with an external mixing chamber is proposed.