OVERVIEW OF STEAM TRAP SURVEY AND MANAGEMENT
Inspect Steam Traps for Efficient System
Faulty or inoperative steam traps can cause losses of hundreds of thousands of Currency. Unfortunately, when it comes to steam traps, people often ignore them.
The hard reality of a plant maintaining its boiler and forgetting about the rest of the steam system can be a horribly wasteful proposition.
Losses can include not only wasted energy but replacement of damaged equipment and misuse of man-hours. It is not uncommon to discover system losses in the hundreds of thousands of dollars.
Fortunately, much of these potential losses can be averted by a vigilant steam management system that includes a program for steam trap surveys. A steam trap survey creates a window into a steam system. Once a maintenance engineer can see what is going on, he or she can take corrective action. Corrective actions can add substantially to a company’s bottom line as “found money.” In some business circles, it has been estimated that $10.00 in-house savings is the equivalent $1,000 in sales. In other words, if a steam system generated $10,000 in savings, it would be the same as achieving $1 million in sales for that company.
In order to create savings by producing steam system efficiencies, it is important to understand the basics of a steam system. Steam loss can occur in both the supply and return side. Such elements as pipe layout, slope angles, sizing and trap type all contribute to the effective use of steam. Many plants have personnel who work on and understand steam systems including traps. Unfortunately, there are also many facilities that do not. These facilities should seriously consider assigning some personnel to be trained in steam system function or obtain the services of steam system experts for advice.
What is a steam trap?
Simply put, steam traps are automatic valves that release condensed steam (condensate) from a steam space while preventing the loss of live steam. They also remove air and non-condensables from the steam space. Steam traps are design to maintain steam energy efficiency by performing specific tasks such as heating a building or maintaining heat for process. Once steam has transferred Btus and becomes hot water, it is removed by the trap from the steam side as condensate and either returned to the boiler via condensate return lines or discharged to atmosphere (a wasteful practice).
When a trap fails?
Most traps fail in the open mode. When this occurs, at times, a boiler may begin to work harder to produce the necessary energy to perform a task which, in turn, can create high back pressure to the condensate system. This inhibits the discharge capacities of some traps, which may be beyond their rating, and cause a system inefficiency. While most traps operate with back pressure, they’ll do so only at a percentage of their rating, affecting everything down the line of the failed trap. Steam quality and product is affected.
A closed trap produces condensate back-up into the steam space. The equipment will not produce the intended heat. As an example, if there are four coils in a dryer and only three are operating, it will take longer for the dryer to dry a product, which will have a negative effect on production.
How failure affects equipment?
When steam traps cause a back-up of condensate in a steam main, the condensate is carried along with the steam. It lowers steam quality and increases the potential for waterhammer. Not only will energy be wasted, equipment can be destroyed.
Waterhammer occurs as slugs of water are picked up at high speeds in a poorly designed steam main or in pipe coils or where there is a lift after a steam trap. In some systems, the flow may be at 120 feet per second, which is about 82 m.p.h. As the slug of condensate is carried along the steam line it reaches an obstruction, such as a bend or a valve, where it is suddenly stopped. The effect of this impact can be imagined. It is important to note that the damaging effect of waterhammer is due to steam velocity, not steam pressure. It can be as damaging in low pressure systems as it can in high. This can actually produce a safety hazard, as a valve or a strainer can be blown out by the force of waterhammer.
Before testing a steam trap, inspectors should be familiar with the particular function, review typical types of traps and know the various pressures within the system. This can help avoid misdiagnosis and allow proper interpretation of trap conditions.
There are three main categories of online trap inspection: visual, thermal and acoustic. Visual inspection depends on a release valve situated downstream of certain traps. An inspector opens these valves and looks to see if the trap is discharging condensate or steam. Thermal inspection relies on upstream/downstream temperature variations in a trap. It includes pyrometry, infrared, heat bands (wrapped around a trap, they change color as temperature increases), and heat sticks (which melt at various temperatures). Acoustic techniques require an inspector to listen to and detect steam trap operations and malfunction. This method included various forms of listening devices such as doctors? stethoscopes, screwdrivers, mechanical stethoscopes and ultrasonic detection instruments.
The ideal listening device will allow users to listen to the sounds of steam trap operations while ignoring most ambient pipe sounds. This is where ultrasonic listening devices excel. Since they are sensitive to high frequency (short wave) signals, they tend to ignore most stray pipe signals. Also, they are very directional in their pick-up. For this reason, they will allow users to hear and see on meters the exact operations of steam traps.
Ultrasonic detectors usually have a stethoscope module, which contains an ultrasonic transducer attached to a metal rod that acts as a “wave guide”. The wave guide is touched on the downstream side of a trap to determine trap condition such as mechanical movements or steam and condensate flow. Most ultrasonic detectors amplify the signals and translate them into the audible range where they are heard through headphones or seen as intensity increments on a meter and recorded or stored a sound wave for further spectrum analysis with software to analysis the health status of traps.
Good record-keeping is essential. It is one thing to just inspect traps, another to be able to determine costs, efficiencies, inefficiencies and trouble spots. To begin with, traps should be tagged and mapped. All too often many traps in a system are forgotten. A mapping and tagging system will assure that these traps are maintained.
There are many ways to systematize data and to keep records. The result should be useful records such as cost analysis of the work performed. Also, analytic ability is needed to determine the status of all the traps within a system including those failed, blocked, leaking, out of service or operating well..
Outsource survey ideal
Professional services can conduct surveys and issue reports without involving in-house staff. Or in facilities with large staffs, an expert can be brought in to set up a program and train personnel. In-house staff can be trained to maintain and inspect traps while the professional can assure that the program runs effectively.
In summary, any plant with a steam trap system should set up a comprehensive survey program. Whether it has 50 traps or 5,000 traps, substantial savings can be generated in the energy, equipment, man-hours and product by keeping on top of the system.
ESTIMATING THE COST OF STEAM LOSS THROUGH THE ORIFICE OF A STEAM TRAP
Investigation of steam loss in a steam system, or routine or preventive maintenance procedures, may reveal that one or more steam traps are leaking. How does the cost of repairing or replacing the defective steam traps compare to the value of the lost steam?
When a steam trap malfunctions, steam in form of vapor escapes through the outlet valve or orifice. The steam that escapes is wasted energy that cannot be recovered. By determining the amount of steam that escapes, it is possible to determine the financial loss and whether or not a trap maintenance and repair program would be beneficial. Steam loss through an orifice can be estimated using a variant of the Napier formula:
Steam Flow (lb/hr) = 24.24 x Pa x D²
where: Pa = Pgage + Patmospheric
Pa = Absolute Pressure, psia
Pgage = Gage Pressure, psig
Patmospheric = Atmospheric Pressure, psi = 14.696 psi
D = Diameter of Orifice, in.
Pgage = 5 psig
Pa = 19.696 psia
D = 0.1875 in
W = 24.24 x 19.696 psia x (.1875 x .1875) = 16.78 lbs/hr
ESTIMATING ANNUAL FUEL COST PER STEAM TRAP
For a trap that is leaking continuously throughout the entire heating season, the cost for the loss of steam in the trap can be determined using the following formulas:
Formula for Annual Fuel Cost per Trap – Using Cost per MMBtu in Natural Gas in Commercial Heating Systems:
Q = L x H x E x 10-6 x C/ BE
where: Q = Energy Lost ($)
L = Lb/Hr of steam lost = 16.78 lbs/hr (0.187” orifice, 5 psig)
H = Hours in heating season = 5,808
E = Latent heat of steam at 5 psig = 960.8 Btu/lb
10-6 = MMBtu/Btu
C = Cost of gas per million Btu = $6.23
BE = Boiler Efficiency = 80%
Q = (16.78) (5,808) (960.8) (10-6) (6.23)/0.80 = $729.20
If a steam trap maintenance program were to be implemented and the cost to repair or replace each defective trap were known, the Equipment Cost for the project can be determined as follows:
Equipment Cost = Cost per Trap x Number of Traps
The Cost per Trap is: 3/4” Float and Thermostatic Trap = $ 65
1 hour labor = 35
Cost per Trap = $100
Calculating the Equipment Cost for one trap:
Equipment Cost = $100 x 1 = $100
Simple Payback (years)
The Simple Payback in terms of years is beneficial in determining the financial return of the proposed trap maintenance program. The quicker the payback, the more a project can be justified.
Simple Payback = Equipment Cost
Using the Annual Fuel Cost per Trap ($/M-Lb) and the Equipment Cost from above, the Simple Payback can be determined:
Simple Payback = $100 / $729.20
= 0.1371 years or (1.645 months)
Figuring a total annual energy savings of $729.20 and an equipment cost of $100 for a new trap, the savings acquired from the replacement of just one trap would be enough to pay for 7 new traps
This is an example of the cost effectiveness of implementing a steam trap preventive maintenance program where traps are inspected, maintained, repaired and replaced on a regular basis.
Adding Value in bottom line of profit by Establishing and Maintaining a Continuous Steam Trap Management Program.
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