8 replies to this topic

[steamreformer]

Dear members,
this is my first post i am looking after steam blowing calculations ,how much steam is required to blow a line of 10inch dia and 20 m long.i shall be highly thankful to any one of you who has doen thse calculation please try to help me .
regards
ali

[steamreformer]

i am still waiting for some great chemical engineer to solve my problem. dear art where r u ? plz come to my rescue..

[djack77494]

ali,
I don't know what you are looking for. Are you using the steam blowing to purge the line? Perhaps to obtain some maximum oxygen content? Please clarify the purpose of this operation.

[steamreformer]

Dear sir,

first of all i am very happy to see ur reply as after 3 days some one come to see that and drop me a reply.

sir, i have to calculate the amount of steam required to do the target steam blowing of new HP steam lines up to turbine inlet. we are using target plate method for that.
generally up to turbine inlet we did steam blowing to remove the grease /dust and other materials. its not for purging as u doubt. if u have these calcs in excel sheets plz mail me. i am thankful to u lot sir..

my line is 10 m long and 12 inch dia

[Art Montemayor]

Ali:

As Doug has pointed out, it is terribly important for the Forum to receive ALL of the story and facts about what you intend - or plan - to do. If we don't get all the facts up front, we all tend to wander off in different directions with out perceptions about what you need.

Now that we have the rest of the story (all of it, I hope), it is clearer about what an experienced engineer would normally do in your case:

You are commissioning a steam turbine and have to blowout the inlet feed steam line in order to remove as much debris, trash, dust, or other foreign matter that may be in the line before startup. You will insert a startup strainer before the steam turbine after the blowout - to continue to protect the turbine even after startup.

You have now reduced the length of the stated line by 50% - down to 10 meters. No matter what the length, the engineering criteria in such a process is one of good, experienced judgment and common sense. Bear in mind that your objective is to protect a very expensive and delicate piece of equipment. Steam is cheap compared to the turbine. Good engineering judgment dictates that you dedicate as much steam flow as you can afford (which should be a lot - based on a 12" pipe size) and for as long a period as you can tolerate. This is not a question of a calculation. This is common sense engineering. You obviously have a large amount of steam available for the turbine. Otherwise you wouldn't be starting it up. You want to generate as much velocity as you can generate (& tolerate safely) in order to literally "blow out" all the debris that is in the 10 meters of pipe. We all know you have the design steam capacity of the turbine available; try to get more than that if you can to ensure you do as thorough a job as you can. This is downright dirty, LOUD, and maybe hazardous - if you don't design for disposing of the exit steam (+ debris) correctly and safely. Don't forget that you are blowing this steam OUT TO ATMOSPHERE. There will be people in the surrounding area. This must be done safely.

Forget about any theoretical steam blowing calculations and just go out there and do a SAFE and THOROUGH job. Good Luck.

[fallah]

Dear Art,
How about the calculation basics of consumed steam in vessel/tank steam out operation?
Regards

[Art Montemayor]

Fallah:

I believe that you are confusing the application of a "blow-out" with that of a "steam out". Both Unit Operations are very different and rely on different concepts. A blow-out uses the kinetic energy of a fluid to literally and physically entrain and blow out solid and liquid debris within a pipe line. This is rarely, if ever, done on a vessel. The reason for the application on a pipe line is that a high velocity – resulting in a high kinetic energy – can be readily obtained and sustained.

A steam out employs the heat content of steam to break down tars, gums, sludges, and other viscous contaminants within a vessel (or a pipe line) in order to reduce their viscosity and allow them to dissolve or be drained away in order to clean out the vessel or pipe line. In so doing, a slight amount of excess steam is continuously allow to vent in order to maintain a slight positive pressure within the tank. This venting is one way to avoid the creation of a partial (or total) vacuum within the vessel or pipe. The creation of a partial or total vacuum could cause, in many cases, a dangerous hazard to the operation and to the personnel involved. Calculations can be done to avoid a vacuum creation because the thermo properties of steam are known.

In order to try to carry out calculations for a blow-out you would require to know:

1) The quantity, size, shape, type, and weights of all the debris within the pipe line.
2) The location and placement of all the debris inside the pipe line.

I seriously doubt that this information is known - or can be obtained. While the theoretical calculation of such a problem might be an interesting past time for a theorist or scientist, it simply represents a waste of useful time for a pragmatic and practical engineer who has to produce a profitable operation. We know that, if required, we can produce near-sonic velocity conditions for the steam inside the pipe. If that level of velocity cannot entrain and literally "blow-out" the debris, the problem is far greater than what is described and calls for more expensive and time-consuming solutions. I have to assume that the decision that a steam blow-out can successfully be applied has already been done. That being the case, then the next step is to do it – without wasting time on calculations that are based on unknowns.

[fallah]

Dear Art,

Thanks a lot for your valuable explanations. It was better I would submit my request about steam out in a new topic.

Regards

[sathyan srinivas]

hi

As most members pointed out, it is simply a commonsensical step. Though debris plays havoc in a turbine, one cannot be sure of the amount flushed out. The more logical question must be whether you are going to do a single flush, or start-stop-start steps. As for the estimate of steam required, even if you can find that, you will not be sure of complete removal of debris and other unnecessary stuff inside. Thumb rule is steam velocity must be more than settling velocity of densest material inside, and then give 3-4 four complete pipe volume sweeps.