Huge steam losses in the summer 2

[onuigbo]

My summer steam losses (low load)are much higher than my winter losses (20% higher) under the same operating pressure but lower load. I thought my losses should be lower since my load is much lower in the summer (from 220,000 pph to 90,000 pph) at the same pressure of 100 psi. Can somebody explain this apparent discrepancy?. My meters operate poorly at lower loads, and there's more rain in the summer that makes my steam to condense faster, apart from these, what other factors could be responsible for these huge summer losses? My boss would kill me if I don't figure this out.

We deliver steam as if your life depends on it.

 

[katmar]

Hi TBP,

I did not mean that the superheat would be a process problem - only that it would affect the density and the measured flowrate if the meter was not compensated for temperature.

What sort of meters allow "a large portion of the load to sneak past, without reading it"? I am not an instrument engineer, but I would expect an orifice, annubar or vortex meter to be linear (after square root extraction where necessary) to within 0.5% over a 3:1 turndown ratio. Any intrument guys able to comment?

 

[rmw]

TBP, and Katmar,

I am not now a controls engineer now, but I once was. Unfortunately that was a long time ago when the only way to get an accurate flowmeter that would maintain its accuracy through out a real life range of turndown, was to use a pressure compensated ring balance Hagan Flow Meter.

I can't picture those mercury filled cadillacs being PC right now.

I have to rely on the controls guys now to put the best flow metering in, and in that regard, I would suggest to TBP that you post a thread in the controls forum asking specifically for advice on a pressure compensated flow meter for your steam service and turndown range.

Katmar, your general question in the previous thread is a valid controls forum question as well, and I would love to see the answers you would get there in case those guys aren't reading this thread.

rmw

 

[TBP]

The plant I ran was a privately owned central steam plant, and the meters were THE revenue stream. It's been several years, but vortex shedders were the meters of choice, both for accurancy, and turndown.

The pressure compensation is often not a huge factor, but when you've got money changing hands, based on a steam meter reading, it had better be dead accurate. Little old ladies in the customer's accounts payable depts will challenge you to a knife fight in the alley over what they precieve to be $10 descrepency in the steam bill. Ask me how I know that... Put the pressure compensation in, because it's the cheapest thing to do. You'll spend more time and resources in meetings explaining WHY you didn't do it, then the installation cost. If you're downsizing meters (and that's very likely), install a pressure gauge at the pressure transmitter for the compensation. If you don't, you'll get blamed for every problem in the building, because "this new steam meter is too small..." With the gauge in place, you can walk the complaining party a few feet downstream of the meter, and show him that there's lots of pressure available. Any problems he's suffering are NOT related to the meter size. Again, ask me how I know that...

 

[quark]

If the pressure is constant during summer and winter as well, I don't think there will be much difference in measured values due to non compensation. As compensation is done after measurement, the error will be same.

But what TBP says, makes a point. Particularly with Orifice meters, 3:1 is a critical turndown ratio and accuracy may be erratic at the lower range. It may seem, initially, that you are measuring at the lower range of 90000 pph(well in the ratio of 3:1) but there are fair chances that it may be 70000 pph or so and the meter is measuring 90000 pph. In this region the ordinate(accuracy) forms an asymptote with the meter curve.

 

[TBP]

Steam system pressures can (and do) fluctuate for a variety of reasons. Metering steam is tricky business. If you're metering steam as the revenue stream for your business, it's even trickier, because there's a dollar value attached, and you'll have to defend this figure on a regular and on-going basis. On paper, the differences between pressure compensated metering, and non-pressure compensated metering look pretty small. It's difficult to convince people how a, say, 5% error is too small to care about when the accuracy of a $100,000 steam bill is being questioned. The $5,000 in question very likely is all of the profit, or possibly even more, from this customer. Even more important, in the district steam business, your metering accurancy is your credibility.

One of the things I learned from working in the district steam business for over 10 years, is that most existing steam meter installations are inaccurate, to say the least. The most accurate ways to go (5 or 6 years ago, anyway) are pressure compensated vortex shedders, or, when possible, drum style condensate meters. If you really want to see just how crappy most steam meters are, meter the condensate that has already been metered as steam. That's a real eye-opener. You can easily have a 20% error. The outfit I worked for operated a number of district heating operations, and a lot of people spent a considerable amount of time and effort to determine how to accurately meter steam. The end result, was properly sized vortex shedders with pressure compensation.

Steam metering is very much a "go big, or stay home" situation. Install the pressure compensation.

 

[onuigbo]

I am evaluating a proposal for steam losses in a buried pipe, 8 feet underground, pipe length is about 500 feet and pipe size is 12 inches. Steam temperature in pipe is about 293 degrees fahr. Can somebody assist me with the k-value for soil (clay) or does anybody have a formula for computing the heat loss in a buried pipe, or a formula for computoing the k-value or R-value for soil (clay).

We deliver steam as if your life depends on it.

 

[poetix99]

Even though your current question is obviously related to the question which started this thread, please do consider starting a new thread:

* Others with particular knowledge related to the new question might more easily notice a new posting.
* It will also be easily for others to find the new thread in any subsequent "searches" of this site.