Technical Discussions

Matrix Resolves a Lot of the Questions about Venturis Here

Matrix is a specialist when it comes to venturi steam trap technology. We’ve learned from the top venturi technicians and engineers in the world. And we have developed a practical understanding of many of the issues companies are faced with when it comes to the distribution of steam and the return of condensate. We know when, where and how to utilize venturi steam technology in various steam systems, with unprecedented success, saving customers $ Millions!

The bad news is that venturi technology is either not taught or not properly taught at many engineering schools, and many steam industry “experts” bad mouth the technology. The good news is that we haven’t let the nay-sayers, the other steam trap companies, or the schools stop us from working with and using the technology to save our customers Millions of dollars!

When properly sized and installed, venturi steam traps are amazingly effective and flexible. Let us show you how we may be able to save you $Millions using venturi steam traps.

Steam Systems, Heat Transfer, and the Fixed Orifice 

In steam systems when there is heat transfer condensate is generated. Various systems have been developed over the course of time to eliminate that condensate from steam systems and hold back or trap the steam. Most of these steam traps use large orifices with a door to block the orifice once the condensate has been removed. Because these steam traps use moving parts they break down over time.

With most steam systems the rate of heat transfer is predictable and can be calculated such that an orifice can be found to closely match the condensate flow. This level of steam system analysis allows Matrix to offer a more cost effective, productive, efficient, and reliable alternative approach to removing condensate and trapping steam.

Matrix can size the orifice to optimally release the condensate and simultaneously block the release of steam. This allows Matrix to eliminate the moving parts, thus offering a permanent solution that can be qualified in most industrial applications.

The Matrix Venturi

In addition to identifying an optimal size orifice for eliminating condensate for a steam application, Matrix takes advantage of the well-known venturi effect to extend the working range of loads that can be handled by a fixed orifice.

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The Matrix venturi is a stainless steam unit shaped like a funnel that constricts the flow of steam and condensate, thus adding turbulence to an already turbulent environment upstream of the orifice. This turbulence and the venturi effect allow Matrix to hold back steam even when the orifice is only partially filled or occupied with condensate. This allows Matrix to handle a wider variation of load at a given pressure than can be done with a simple orifice.

Technical Topics

How Venturis Work

Venturis may be simple, but how they work is not. A fluid accelerates and drops in pressure through a venturi. Normally, part of the orifice is filled with flowing condensate. If the percentage of occupancy is less than 100%, why doesn’t steam leak out?

Here’s why: Some hot condensate flashes into steam as pressure drops through the venturi and into the lower pressure return system. The backpressure of this rapidly expanding flash steam blocks supply steam leakage.

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An orifice that is at least 68% occupied by condensate will lose no measurable steam. This covers nearly all production applications. So how do venturis work when occupancy is below 68%? What about startup conditions?

Efficient condensing steam equipment should send very wet steam and condensate to the trap. Venturis are sized to pass the maximum condensate load possible plus a 15% safety margin so that flooding never occurs. During normal operation and for most applications, the venturi orifice is more than 68% occupied and no steam is lost.

Inefficient condensing steam equipment may send dryer steam through the venturi, and the orifice occupancy may fall below 68%. A small amount of supply steam now rapidly expands through the venturi in addition to flash steam. The backpressure of this gas expansion blocks most of the steam from escaping.

The venturi operates on the basis of turbulent flow. When the load drops below 68% capacity, the orifice passes a violently turbulent mixture of equivalent volumes of steam and water. Steam, several hundred times lighter than condensate, tries to pass through the orifice at close to the speed of sound, but is impeded by any condensate present. The steam continuously forces the much denser condensate (traveling about 48 kph) into the orifice, effectively blocking the steam from passing through.

Venturis - Paradigm Shift

Once a plant has been converted to our permanent condensate removal system, the energies are balanced for the first time and the system is pressurized. There is no over-pressurization in the return, water hammer goes away, and traps no longer freeze.

Matrix venturis offer clients an alternative to flappers (pulsing, mechanical traps with moving parts, destined to fail over time.)

Matrix venturis are made from 316 stainless steel and are designed to be a permanent replacement for pulsing steam traps.

In a steam system, condensate is continuously being generated. Matrix venturis are continuous flow. As a result, venturis do a better job of condensate removal from the system.

Most applications qualify for Matrix venturis. In general, loads are predictable and the variations in the loads at a given pressure are known, allowing for accurate sizing and use of venturi steam traps.

Matrix venturi steam traps produce great results with both retrofits and new construction. With retrofits, Matrix works with the client to establish a solid test protocol in order to measure the results in improved performance. With new construction, Matrix works with the design engineer as a specialist consultant to ‘bless’ the applications.

Some of the secrets of Matrix’ success:

• Matrix performs a Steam System Analysis to build a complete profile of the plant and all of the key steam-related issues, including lift in the return.

• Matrix converts the boiler header traps and all of the distribution drip legs to the heat transfer equipment.

• Matrix converts the whole system as opposed to a partial conversion.

• Matrix individually traps each coil.

• Matrix provides Design Consulting, Advanced Project Management, Installation Support and Post Installation Inspection Services to ensure a successful, problem-free conversion.

How Matrix Venturis Work with Varying Loads

Large process applications will usually rely on a modulating control valve to vary the load. A modulating valve allows nozzle capacity to vary with pressure differential. When more heat is needed, the control valve opens to increase steam flow, providing greater pressure differential across the nozzle as well as higher nozzle capacity. When demand drops, the control valve closes and pressure and condensate load are reduced.

The range between maximum and minimum flow through a control tends to form a linear relationship such that an orifice size can be found that works for both extremes and everywhere in between without increasing the steam losses to unacceptable levels.  At maximum pressure where there is maximum heat transfer the maximum condensate load is generated. Matrix can size an orifice to handle this pressure and condensate load. Then when the control is modulated to the minimum pressure there is minimum heat transfer which generates the minimum condensate load. The same size orifice used for the maximum load will handle this minimum extreme.

Full Plant versus Partial Conversion

In some large installations and in some very busy smaller installations it makes logistical sense to convert systems to venturis steadily over time. Matrix has worked with several industries where some have converted all at once and some have converted more slowly over time or only partially converted. What have we learned from this experience?

Most systems that convert all at once or steadily over a reasonably short period of time have reported great results in reliability, efficiency, and productivity. The results get better the further along the conversion proceeds.

Systems that convert only partially for one reason or another, have sometimes (not always) produced mixed results. Matrix has gone back to these problematical partial installations to analyze the situations for root causes. These fall into the following categories:

  1. Applications converted to venturis work fine, but fall short of the expected results.(e.g. sawmills that convert a few of their kilns but not all)
  2. Applications converted to venturis work fine, no measurable results – diluted by all of the other traps that have not been converted. (e.g. paper mills that replace only bad traps and not by sections)

Mixing pulsing (mechanical) traps with continuous flow venturis in some cases can reduce the optimal performance of venturis, especially if the mechanical traps are not maintained or when the steam supply is limited and constrained.

Mechanical Traps not Maintained

If a mechanical trap is leaking or blowing it effectively turns into an oversized orifice trap with the accompanied excessive steam losses. This blowing trap when competing with the venturi can do several things. The blowing trap can over-pressurize the return, reducing the pressure differential across all of the affected traps. In some of these cases the problem is exacerbated because the return line is undersized.

What Happens to Venturis When Return is Over-Pressurized

Because venturis are sized for efficiency with a definite pressure differential, this over-pressurized system negatively impacts the sizing of the venturi. We’ve seen reports of some reduced output under this competition as well as some claims of flooding of the coils with the venturis. The problem is not the venturis, but the blowing mechanical traps.

Once the return is over-pressurized, the pressure differential across the venturis is reduced, effectively reducing the heat transfer capability of the venturi. The venturis seem to be doing a poorer job when the fact is that they are using what steam they do get more efficiently.

All steam traps are designed to work at a specified condensate load and pressure differential. If the robbed supply to venturis gets very bad then we are also trying to operate with a reduced differential. This could back up water unnecessarily.

Distribution System not Converted

When the boiler header and distribution system are not properly trapped, wet steam is delivered to heat transfer equipment. This negatively affects the performance of the process equipment. The wet steam has reduced heat transfer capability, reducing performance of the equipment. (Matrix covers this in great detail in their technical presentations) Additionally, there is increased condensate that has to be handled by the steam trap attached to the process. We size our venturis for optimal efficiency at this process equipment. We require dry steam at the inlet of the process in order to deliver optimal performance and optimal efficiency.

Constrained Steam Supply

In plants with limited steam supply, blowing traps can drain this supply and push the boiler past 85% capacity. After this point there is both an increase of carryover (contaminants being entered into the distribution main) and a sagging in pressure output.

Equipment making demands on this system can compete for supply. In systems with mixed mechanical traps and venturis, the bucket traps are capable of robbing the supply and the performance of the venturis is negatively impacted. The orifice of the venturi is sized for optimal performance and can deliver both efficiency and productivity. Mechanical trap systems are capable of interfering with this optimal performance.

Combined Effect of the Pulsing Action of Mechanical Steam Traps Results in Sporadic Disrupts to the Condensate Return Flow

The pulsing action of mechanical traps results in stop start action of condensate throughout the steam distribution and return system.

In the supply there is more condensate and the condensate is being pushed along by the steam, with more condensate passing over the drip legs when the traps are closed than would be the case if there was a venturi there always open with its nozzle effect drawing on the condensate.

In the heat transfer equipment the condensate is more sluggish when the trap is closed and then is pushed out with a blast of supply steam when the trap opens. With the venturi there is continuous flow through the heat transfer equipment resulting in more consistent heat transfer.

In the return each pulse of the mechanical trap pushes the condensate along briefly and then stops, resulting in a sporadic return flow, sometimes hammering from a collapsing steam bubble and sometimes stalled. If there are leaking and blowing traps, add over-pressurization to the mix.

With a venturi system everything is moving more consistently, System is pressurized for steam but always open for condensate. The venturi effect causes even distribution flow, optimal heat transfer with a steady flow of condensate through the process equipment and a peppier but properly pressurized return flow with no hammering (no steam bubbles).

Comparing Matrix Venturis to Mechanical Traps

A brand new mechanical steam trap will lose more supply steam than a properly sized Matrix venturi.

A failed conventional trap, according to the Department of Energy’s ‘Leaking steam trap discharge rate’, with a .05 cm (1/8″) opening loses 24 kg/hr (52.8 lbs/hr). A venturi sized for the same application would lose under .8 kg/hr (1.76 lbs/hr).

If it is operating properly, a mechanical steam trap with its significantly larger orifice opens and closes about 6 times a minute.  Each time the mechanical trap opens there is a small pressure drop. This can be demonstrated at any plant.  While the pressure drop is small, in a system with 100 traps, this equals 36,000 small pressure drops every hour.

The permanent Matrix venturi system eliminates these pressure drops, improving heat transfer in the system.

Matrix venturis have no moving parts to fail.

Mechanical traps remove condensate cyclically.  Because they are constantly opening and closing, they wear, leak and then fail.

Matrix venturis improve heat transfer in process equipment.

The venturi system removes condensate with a continuous flow that happens so rapidly that there is virtually no time for the condensate to cool and collect in the steam coils.

Steam is heat and water, and when the heat is lost, steam turns back to water.  In steam systems with mechanical steam traps, when heat from steam is lost, vapor condenses to the bottom of the pipe and finally makes its way to the mechanical trap.

With our permanent venturi condensate removal system, the constant change in pressure and the continuous flow result in significantly less condensate on the heat transfer side of the equipment.  The BTU count is higher in the heat transfer chamber and condensate isn’t acting as an insulator.  Condensate is eliminated from the system immediately.

Water hammer, corrosion and other problems caused by excess condensate in the system will be greatly reduced, making the work environment safer.

The Choice between Matrix Venturis vs. Mechanical Traps

If you had a choice between two tools with one being permanent and the other lasting only a few years and the cost was the same, which one would you chose?

When it comes to choosing for your steam system between permanent venturis and mechanical traps which are not permanent the choice is similar. The main challenge then is to establish whether both options are viable and are the costs agreeable.

Qualify the applications one at a time to determine if the venturi option is viable. A vast majority (98%) of the time they are. This can be corroborated by reference and by pilot demonstration.

Converting to a venturi system will require some repiping, but it is usually not more than replacing a mechanical trap and in some cases simpler and cheaper, so replacing a mechanical trap with a Matrix venturi is generally cost-effective.

Matrix Venturis versus Less Expensive Mechanical Traps and Universal Connectors

In some cases, e.g. tracing systems with disc traps, failure occurs so regularly that manufacturers have taken measures to make repair simple and inexpensive. In these cases, how does converting to a Matrix venturi system stack up?

Matrix has analyzed the situation for today’s tracing systems as follows:

Over the course of 15 years (the warranty period of a Matrix venturi) how many replacements of a disc trap will be required, because the trap is failing open or closed or it is leaking excessively? If the failure rate is one or two years for a disc trap the comparison looks like the following:

  1. Trap is failing but neglected for a year or more – leads to significant steam losses.
  2. Trap is repaired (at some cost) or replaced regularly (annually or biannually).

Steam losses under case 1) can be estimated and compared to venturis with the result being favorable to venturis. The cost of fuel can be factored into the decision and the ROI determined.

Trap repairs under case 2) that occur on a regular basis can also be costed out, including both parts and labor. Once again the calculation can be done for the ROI.

It would be wise in either 1) or 2) above to also Include the impacts of other costs, i.e. lost production due to down-time; wear and tear on piping and other equipment. In some cases safety issues and impact of freezing can be factored in as well. All in all a typical payback for a tracing system is estimated to between one and four years.

Short-Circuiting

When coils or zones are not individually trapped, a phenomenon called ‘short circuiting’ can occur.

Two coils may be identical or nearly identical, but loads are almost never perfectly balanced. It doesn’t take much of a difference in heat transfer to generate a difference in load and pressure at the outlet of the trap. This could be a result in a series of coils sharing a common fan air flow, where the first coil gets hit the hardest and generates the greatest load. Then the warmed air hits the secondary coil, such that reduced heat transfer occurs resulting in lower condensate load and higher pressure at the outlet.

With even a subtle difference in loads on a pair of ganged coils, the small differences in pressure are significant enough to cause a back flow into the coil with the lower pressure. This results in fluctuations in the ganged coils that interfere with optimal heat transfer, cause fluctuating cold spots, and damage the coils over time because of the flooding.

Every coil or zone should be individually trapped, and loads should be as balanced as possible.