Calculation of DISTURBANCE FACTOR for Steam Blow out

[adeliry]

Dear friends,


We want to remove sludge and debris of steam pipe lines by steam blowing method.

If we want to have a efficient steam out as it said before, disturbance factor must be higher than 1.2.

Normal operation condition of pipe line is:

Pressure :22 bar

Flow rate: 175 ton/hr

Temperature: 245 oC

we don't have enough steam to reach 1.2 by increasing flow rate and therefor only way is to decrease pressure to have higher specific volume.

I want know when we blowing steam to atmosphere, and we have 22 bar steam at supplied point, which pressure must be applied to calculate specific volume?( atmosphere?, supplied pressure?, average of them? or we must apply a pressure gauge to read real pressure? ( in latest case where gauge must be installed? near the outlet temporary line or inside loop?))

Also how much we can decrease the pressure to reach enough specific volume? is there any limitation? for example we will have 80 ton/hr 22 bar steam during steam blow out and we must decrease the pressure to 13 bar to have disturbance factor equal to 1.2. is it safe or may be we will face with strong hammering?

only way to decrease the pressure is using the supply valve (globe valve) to break down the pressure. is it the right method or not.?

I will be thankful for any early response.

 

[macmet]

When I do steam blows I use the pressure measured in the pipe which is only a result of the back-pressure (usually) generated during the blow as we discharge to atmosphere. Of course this causes problems with water consumption and we're now looking at closing the loop at one of our upcoming projects.

You may have better options as our application is part of commissioning. There are a few contractors out there that have a lot of experience with different types of blows. I've only seen the type specific to our product.

 

[adeliry]

Dear macmet,

Thank for your reply.

But there is another question.
It seems that 2 methods applied to steam blow out. in firs method a sacrifice valve positioned at the end of pipeline and before temporary line ( valve must be quick open type) and after pipe filled with steam up to desired pressure, sacrifice valve will be opened and for some minutes (5-15 minute)steam is blown with maximum rate that boilers can provide without loss of water level at steam drum.

in second method, that is continuous, a low pressure steam with high flow is blown from pipe without any valve at the end of pipeline and after 1-2 hour supply valve of steam is closed and it is allowed till pipe line cooled and because of contraction and latter expansion , scaled and debris dislodged from pipe and this is repeated until we have a clean pipe.
in the first method if we install a pressure gauge at the pipe line we able to read constant pressure across the pipe but in second method we have a pressure profile that is high near the supply and is low near the outlet at temporary pipe. if we install a PG, where is the right place for installing ( start of loop, mid point or end point)?

 

[adeliry]

Dear macmet,

Thank for your reply.

But there is another question.
It seems that 2 methods applied to steam blow out. in firs method a sacrifice valve positioned at the end of pipeline and before temporary line ( valve must be quick open type) and after pipe filled with steam up to desired pressure, sacrifice valve will be opened and for some minutes (5-15 minute)steam is blown with maximum rate that boilers can provide without loss of water level at steam drum.

in second method, that is continuous, a low pressure steam with high flow is blown from pipe without any valve at the end of pipeline and after 1-2 hour supply valve of steam is closed and it is allowed till pipe line cooled and because of contraction and latter expansion , scaled and debris dislodged from pipe and this is repeated until we have a clean pipe.
in the first method if we install a pressure gauge at the pipe line we able to read constant pressure across the pipe but in second method we have a pressure profile that is high near the supply and is low near the outlet at temporary pipe. if we install a PG, where is the right place for installing ( start of loop, mid point or end point)?

 

[macmet]

I have seen the pressure gauge in the continuous method at the end of the line.

I'd be curious if anyone has any different experiences with the continuous method.

 

[macmet]

I'm sorry, I was thinking about this last night at home. We have pressure transmitters on both ends of the line. But the PT at the outlet is the determining reading.

We usually aim for a CFR of 1.15-1.2 at the outlet of the pipe. The higher pressure at the inlet will have a CFR slightly higher, but still within the acceptable range.

 

[adeliry]

Dear macmet,

Thanks for your reply.


We do a simulation with Hysys and it shows that after supply valve we have very negligible pressure drop across the pipe line and if we have 1.2 bar at the outlet to atmosphere we would have 1.5-1.6 bar after supply valve, because friction of pipeline and bends is only source for pressure drop. in this case specific volume isn't very different for .5 bar PD.

I surprised that it seems that we need only high flow rate and sufficient temperature to have 50-70 oC above saturation temperature. and we can do steam blowing with 5 bar same as 40 bar steam because in every case supply valve bring sufficient "delta P".

Can you approve this or you have other idea?

 

[macmet]

I have not really looked into the degree of superheat during our steam blows. 50-70C above superheat is lower than we operate our boilers at, but our steam blows are part of commissioning and are done to atmosphere, so low pressure, and high temperature, without concern for superheat. I will look at this next time if I remember.