Steam Blow Calculation

At Steam Blowing Services Ltd (SBS) we generally use two types of SteamBlow.

1. Continious steam blow

2. Intermittent steam blow

With all types of steam blowing, the cleaning is effected by blowing sufficient steam through the components to be cleaned to dislodge and carry out any debris and contaminants that otherwise would be carried into the steam turbine. It is not an absolute cleaning method – and it will not remove all of the contaminants present. Typically, steam blowing will not totally remove very strongly adherent materials such as mill scale. However, all that is necessary is to ensure that none of the material which remains after steam blowing will be carried out during normal operation when the steam is admitted to the steam turbine. To make sure that this is the case the forces on the debris during steam blowing must be higher than those experienced in normal operations. The ratio of these forces is called the DISTURBANCE FACTOR (DF) or CLEANING FORCE RATIO (CFR).

 

                                                         Force during Steam Blowing

      CLEANING FORCE RATIO =    --------------------------------------

                                                        Force during normal operation

 

So, in theory at least, provided that the CFR is greater than one, after steam blowing, no further debris will be released when the plant is put into operation and the steam will be turbine quality.

 

To prove that the steam is turbine quality, two steps are taken. First, calculations are made of the actual CFR achieved during each steam blow. Secondly, the particle content of the steam used for the cleaning is assessed. This assessment is carried out by putting a metal TARGET PLATE in the steam flow, usually at the point where it exits from the system being cleaned. The steam velocities are such that, even very small particles in the steam will produce a visible impact on the metal plate. The turbine manufacturer will produce a specification for acceptable steam quality in terms of the CFR needed during cleaning and the number of allowable impacts on the target plate. SBS use of target plates means that physical evidence of steam quality is produced during steam blowing.