Steam and condensate loop book pdf download

These sensing tubes sense various velocity pressures across the pipe, which are then averaged within the tube assembly to give a representative flowrate of the whole cross section. DP output. Presents little resistance to flow.

Inexpensive to buy. Simple types can be used on different diameter pipes. Turndown is limited to approximately by the square root relationship between pressure and velocity as discussed in Module 4. If steam is wet, the bottom holes can become effectively blocked. To counter this, some models can be installed horizontally. Sensitive to changes in turbulence and needs careful installation and maintenance.

The low pressure drop measured by the unit, increases uncertainty, especially on steam. Placement inside the pipework is critical. Occasional use to provide an indication of flowrate. Determining the range over which a more appropriate steam flowmeter may be used.

Vortex shedding flowmeters These flowmeters utilise the fact that when a non-streamlined or bluff body is placed in a fluid flow, regular vortices are shed from the rear of the body. These vortices can be detected, counted and displayed. Over a range of flows, the rate of vortex shedding is proportional to the flowrate, and this allows the velocity to be measured. The bluff body causes a blockage around which the fluid has to flow. By forcing the fluid to flow around it, the body induces a change in the fluid direction and thus velocity.

The fluid which is nearest to the body experiences friction from the body surface and slows down. Because of the area reduction between the bluff body and the pipe diameter, the fluid further away from the body is forced to accelerate to pass the necessary fluid through the reduced space.

Once the fluid has passed the bluff body, it strives to fill the space produced behind it, which in turn causes a rotational motion in the fluid creating a spinning vortex. The fluid velocity produced by the restriction is not constant on both sides of the bluff body.

As the velocity increases on one side it decreases on the other. This also applies to the pressure. On the high velocity side the pressure is low, and on the low velocity side the pressure is high. As pressure attempts to redistribute itself, the high pressure region moving towards the low pressure region, the pressure regions change places and vortices of different strengths are produced on alternate sides of the body.

The shedding frequency and the fluid velocity have a near-linear relationship when the correct conditions are met. The frequency of shedding is proportional to the Strouhal number Sr , the flow velocity, and the inverse of the bluff body diameter. These factors are summarised in Equation 4. I Vortex shedder Fig. Reasonable turndown providing high velocities and high pressure drops are acceptable. No moving parts.

Little resistance to flow. At low flows, pulses are not generated and the flowmeter can read low or even zero. Lower velocities found in steam pipes will reduce the capacity of vortex flowmeters. Vibration can cause errors in accuracy. Correct installation is critical as a protruding gasket or weld beads can cause vortices to form, leading to inaccuracy.

Long, clear lengths of upstream pipework must be provided, as for orifice plate flowmeters. Direct steam measurements at both boiler and point of use locations. Natural gas measurements for boiler fuel flow. Vortex shedding flowmeter Upstream Flow Downstream. Vortex shedding flowmeter Pressure tap Temperature tap Upstream Flow 3. A 50 mm bore steam pipe lifts up and over a large industrial doorway. An orifice flowmeter is fitted in the horizontal pipe above the doorway, with a 1.

The b ratio is 0. What will be the effect of the straight run of pipe before the flowmeter? Why are turbine flowmeters frequently fitted in a bypass around an orifice plate flowmeter? What is the likely effect of a spring loaded variable area flowmeter installed as in Figure 4. What feature makes the differential pressure type of spring loaded variable area flowmeter suitable for a turndown of ? Which of the following is a feature of the Vortex shedding flowmeter against an orifice plate flowmeter?

Which of the following are an advantage of the spring loaded variable area flowmeter over the Vortex shedding flowmeter? Instrumentation A steam flowmeter comprises two parts: 1. The primary device or pipeline unit, such as an orifice plate, located in the steam flow. The secondary device, such as a differential pressure cell, that translates any signals into a usable form. In addition, some form of electronic processor will exist which can receive, process and display the information.

Temperature transducer Flow Upstream pressure tapping Pressure transducer. Differential pressure cells DP cells If the pipeline unit is a differential pressure measuring device, for example an orifice plate flowmeter or Pitot tube, and an electronic signal is required, the secondary device will be a Differential Pressure DP or DP cell. This will change the pressure signal to an electrical signal.

This signal can then be relayed on to an electronic processor capable of accepting, storing and processing these signals, as the user requires. Upstream pressure cap. A typical DP cell is an electrical capacitance device, which works by applying a differential pressure to either side of a metal diaphragm submerged in dielectric oil. The diaphragm forms one plate of a capacitor, and either side of the cell body form the stationary plates. The movement of the diaphragm produced by the differential pressure alters the separation between the plates, and alters the electrical capacitance of the cell, which in turn results in a change in the electrical output signal.

The degree of diaphragm movement is directly proportional to the pressure difference. The output signal from the measuring cell is fed to an electronic circuit where it is amplified and rectified to a load-dependent mA dc analogue signal. This signal can then be sent to a variety of devices to: o o. The advancement of microelectronics, and the pursuit of increasingly sophisticated control systems has led to the development of more advanced differential pressure cells.

In addition to the basic function of measuring differential pressure, cells can now be obtained which: o o o o o. Can indicate actual as distinct from differential pressure. Have self-monitoring or diagnostic facilities. Have on-board intelligence allowing calculations to be carried out and displayed locally.

Can accept additional inputs, such as temperature and pressure. Many different methods are available for gathering and processing of this data, these include: Dedicated computers. One of the easier methods for data collection, storage, and display is a dedicated computer. With the advent of the microprocessor, extremely versatile flow monitoring computers are now available. The display and monitoring facilities provided by these can include: o o o o o o o o. Current flowrate. Total steam usage.

Steam usage over specified time periods. Abnormal flowrate, pressure or temperature, and trigger remote alarms. Compensate for density variations. Interface with chart recorders. Interface with energy management systems. In addition to the computer unit, it is sometimes beneficial to have a local readout of flowrate. Data collection, whether it is manual, semi-automatic or fully automatic, will eventually be used as a management tool to monitor and control energy costs.

Data may need to be gathered over a period of time to give an accurate picture of the process costs and trends. Some production processes will require data on a daily basis, although the period often preferred by industrial users is the production week. Microcomputers with software capable of handling statistical calculations and graphics are commonly used to analyse data.

The usual means of achieving this is to plot consumption or specific consumption against production, and to establish a correlation. However, some caution is required in interpreting the precise nature of this relationship. There are two main reasons for this: o o. Secondary factors may affect energy consumption levels. Control of primary energy use may be poor, obscuring any clear relationship. Statistical techniques can be used to help identify the effect of multiple factors. It should be noted that care should be taken when using such methods, as it is quite easy to make a statistical relationship between two or more variables that are totally independent.

Once these factors have been identified and taken into account, the standard energy consumption can then be determined. This is the minimum energy consumption that is achievable for the current plant and operating practices.

The diagram in Figure 4. Using the standard, the managers of individual sections can then receive regular reports of their energy consumption and how this compares to the standard. How does consumption compare with the standard? Is the consumption above or below the standard, and by how much does it vary? Are there any trends in the consumption? Poor control of energy consumption.

Defective equipment, or equipment requiring maintenance. Seasonal variations. If there is a variation in consumption it may be for a number of reasons, including: o o o. To isolate the cause, it is necessary to first check past records, to determine whether the change is a trend towards increased consumption or an isolated case.

In the latter case, checks should then be carried out around the plant for leaks or faulty pieces of equipment. These can then be repaired as required. Standard consumption has to be an achievable target for plant managers, and a common approach is to use the line of best fit based on the average rather than the best performance that can be achieved see Figure 4.

Once the standard has been determined, this will be the new energy consumption datum line. This increase in energy consciousness will inevitably result in a decrease in energy costs and overall plant running costs, consequently, a more energy efficient system. Special requirements for accurate steam flow measurement As mentioned earlier in Block 4, flowmeters measure velocity; additional values for cross sectional area A and density r are required to enable the mass flowrate qm to be calculated.

For any installation, the cross sectional area will remain constant, the density r however will vary with pressure and dryness fraction. The next two sections examine the effect of pressure and dryness fraction variation on the accuracy on steam flowmeter installations. In an ideal world, the pressure in process steam lines would remain absolutely constant. Unfortunately, this is very rarely the case with varying loads, boiler pressure control dead-bands, frictional pressure losses, and process parameters all contributing to pressure variations in the steam main.

Following start-up, the system pressure gradually rises to the nominal 5 bar g but due to process load demands the pressure varies throughout the day. With a non-pressure compensated flowmeter, the cumulative error can be significant. Time elapsed hours Fig. Some steam flowmetering systems do not have inbuilt density compensation, and are specified to operate at a single, fixed line pressure. If the line pressure is actually constant, then this is acceptable.

However, even relatively small pressure variations can affect flowmeter accuracy. It may be worth noting at this point that different types of flowmeter may be affected in different ways.

The output signal from a vortex shedding flowmeter is a function of the velocity of flow only. It is independent of the density, pressure and temperature of the fluid that it is monitoring.

Given the same flow velocity, the uncompensated output from a vortex shedding flowmeter is the same whether it is measuring 3 bar g steam, 17 bar g steam, or water. Flow errors, therefore are a function of the error in density and may be expressed as shown in Equation 4. Pressure bar g 4. Use Equation 4. Therefore, the uncompensated vortex flowmeter will over read by Difference from specified pressure bar g Fig. The output signal from an orifice plate and cell takes the form of a differential pressure signal.

The measured mass flowrate is a function of the shape and size of the hole, the square root of the differential pressure and the square root of the density of the fluid.

Given the same observed differential pressure across an orifice plate, the derived mass flowrate will vary with the square root of the density.

As for vortex flowmeters, running an orifice plate flowmeter at a pressure other than the specified pressure will give rise to errors. The percentage error may be calculated using Equation 4. An orifice plate steam flowmeter specified to be used at 5 bar g is used at 4. The positive error means the flowmeter is overreading, in this instance, for every kg of steam passing through, the flowmeter registers When comparing Figure 4. Therefore, density compensation is essential if steam flow is to be measured accurately.

Dryness fraction variation The density of a cubic metre of wet steam is higher than that of a cubic metre of dry steam. If the quality of steam is not taken into account as the steam passes through the flowmeter, then the indicated flowrate will be lower than the actual value. Dryness fraction c has already been discussed in Module 2. For example, a kilogram of steam with a dryness fraction of 0.

Important note: The proportion of the volume occupied by the water is approximately 0. For most practical purposes the volume occupied by the water can be ignored and the density r of wet steam can be defined as shown in Equation 4. Using Equation 4. To reiterate earlier comments regarding differential pressure flowmeter errors, mass flowrate qm will be proportional to the square root of the density r , and density is related to the dryness fraction.

Changes in dryness fraction will have an effect on the flow indicated by the flowmeter. All steam flowmeters will be calibrated to read at a pre-determined dryness fraction c , the typically value is 1. Some steam flowmeters can be recalibrated to suit actual conditions. Therefore, the negative sign indicates that the flowmeter under-reads by 2. It can be argued that dryness fraction, within sensible limitations, is of no importance because: Vortex flowmeters measure velocity.

The volume of water in steam with a dryness fraction of, for example, 0. It is the condensation of dry steam that needs to be measured.

However, independent research has shown that the water droplets impacting the bluff body will cause errors and as vortex flowmeters tend to be used at higher velocities, erosion by the water droplets is also to be expected. Unfortunately, it is not possible to quantify these errors. The steam flowmetering package must include density compensation. Predictable dryness fraction - Measurement of dryness fraction is very complex; a much easier and better option is to install a steam separator prior to any steam flowmeter.

This will ensure that the dryness fraction is always close to 1. With saturated steam there is a fixed relationship between steam pressure and steam temperature. Steam tables provide detailed information on this relationship. To apply density compensation on saturated steam, it is only necessary to sense either steam temperature or steam pressure to determine the density r. This signal can then be fed, along with the flow signal, to the flow computer, where, assuming the computer contains a steam table algorithm, it will then do the calculations of mass flowrate.

However, superheated steam is close to being a gas and no obvious relationship exists between temperature and pressure. When measuring superheated steam flowrates, both steam pressure and steam temperature must be sensed and signalled simultaneously. The flowmeter instrumentation must also include the necessary steam table software to enable it to compute superheated steam conditions and to indicate correct values. If a differential pressure type steam flowmeter is installed which does not have this instrumentation, a flow measurement error will always be displayed if superheat is present.

The flowmeter thinks it is reading saturated steam at its corresponding temperature. With steam at a line pressure of 4 bar g and 10C superheat, the displayed value of mass flow will be If the flowmeter does not incorporate temperature and pressure compensation what is the actual flowrate? A typical DP cell used with a measuring differential pressure flowmeter a Senses the pressure either side of the flowmetering device and relays a corresponding electrical signal to a display processor b Compares the pressure downstream of the flowmetering device with a fixed upstream pressure and volume, and relays the difference by means of a corresponding electrical signal to a display processor c Senses differential pressure across the flowmetering device, and density of the steam at the designed upstream pressure and passes this information to a display processor d Senses changes in pressure upstream of the flowmetering device and relays a corresponding electrical signal to a display processor 4.

Will the display at 4 bar g be accurate if the flowmeter is not fitted with density compensation? The steam in question 4 is thought to be very wet. What effect will this have? A flowmeter measuring differential pressure is installed on a system where the pressure can vary between 20 bar g and 1 bar g.

Which of the following could cause inaccuracy of the flowmeter? Installation The manufacturer should always supply installation data with the product as this will lay down specific requirements such as the minimum lengths of unobstructed pipe to be provided upstream and downstream of the flowmeter. It is usual for the flowmeter supplier to be able to offer advice and relay recommendations regarding the installation requirements of his particular flowmeter.

Statistics show that over a third of flowmeter problems are due to poor installation. No steam flowmeter, however good its design and thorough its manufacture, can cope if little attention is paid to its installation and the layout of the steam system.

Steam quality Dry steam Steam should always be provided in as dry a condition as possible at the point of metering. Module 4. A simple but effective method of drying wet steam is to install a separator upstream of the flowmeter. Entrained moisture impinges on the baffle plates and the heavy droplets fall to the bottom and are drained away via a properly sized and selected steam trap set.

The separator has one other important benefit: Slugs of water impacting on any steam flowmeter i. The separator with its drain trap ensures efficient condensate removal ahead of the flowmeter. But any low points where the steam main rises to a higher level should also have drain trap points that are adequately sized and correctly selected. It is also worthwhile ensuring that air and other entrained gases are removed by fitting an air vent in the steam line.

The separator shown in Figure 4. Clean steam A pipeline strainer Figure 4. This will remove any larger pieces of scale, swarf or other pipeline debris, which would otherwise damage the primary device. The internal strainer device should be cleaned periodically, particularly during the initial start-up of a new installation.

As with any steam pipeline strainer, the strainer should be installed with the body horizontal to avoid creating an accumulation of condensate and hence a reduction in the screening area Figure 4. Maintenance The provision of valves either side of the flowmeter should be considered for isolation purposes, since inspection, maintenance and perhaps even removal for calibration will sometimes be necessary.

Such valves should be of the fully open or fully closed type, which present the least resistance to flow, such as full bore ball valves.

In addition, a valved bypass, or a make-up piece to act as a temporary replacement if the flowmeter is removed from the pipeline, will solve the problem of interrupting the steam supply during maintenance procedures. Both pipework and flowmeter must be adequately supported and properly aligned with a slight fall to the last drain point ahead of the flowmeter.

Pipework should also be properly and effectively insulated to minimise radiation losses and further condensation. Ensure all pipework is adequately supported and properly aligned.

This will prevent waterlogging during shutdown periods and possible problems on start-up. Size the flowmeter on capacity rather than line size. Where a pipe size reduction is necessary, use eccentric reducing sockets. Take care to observe the correct direction of flow. An arrow on the flowmeter body should show this. It is advisable to fit a check valve downstream of the transducer This will avoid possible damage by reverse flow. Do not close-couple the flowmeter immediately downstream to a pressure reducing valve.

As a general rule, a self-acting pressure control should be at least 10, and preferably 25 pipe diameters upstream of the flowmeter.

Do not install the flowmeter downstream of a partially open stop valve. This can lead to swirl, which may lead to inaccuracies. A separator should always be fitted upstream of the flowmeter. This will remove entrained moisture from the steam. Dry steam is required for accurate steam flowmetering. It will also provide some degree of protection against waterhammer impact damage.

The separator should be drained using a float thermostatic steam trap. A full line size strainer with mesh stainless steel screen must be fitted. This will prevent dirt and scale reaching the transducer. This is especially advisable on old or dirty systems where dirt or corrosion is present.

Ensure gasket faces do not protrude into the pipeline. A bellows sealed stop valve may be fitted upstream of the flowmeter. Recommended lengths of clear, unobstructed pipe must be provided upstream and downstream of the flowmeter. The question of leaving sufficient length of clear, unobstructed pipework upstream and downstream of the flowmeter is most important.

This is to prevent the risk of swirl, which can be produced by bends and partially open valves. Some types of flowmeter are more susceptible to swirl than others. Some manufacturers recommend the use of flow straighteners to remove swirl Figure 4. However, it is preferable to do all that is possible to prevent the risk of swirl by providing an adequate flowmeter run since flow straighteners in steam systems can entrain surface water.

It may even be preferable to select a steam flowmeter that is less susceptible to the effects of swirl. Correct sizing of the flowmeter is also essential and most manufacturers will recommend maximum and minimum flowrates for each size of flowmeter. If the flowmeter to be used is smaller than the pipeline into which it is to be fitted, reductions in pipe size should be achieved by using eccentric reducers Figure 4.

This will prevent the collection of condensate at a lowpoint - as would be the result if concentric reducers were used. The reduction in pipe size should be achieved at the nearest point to the flowmeter consistent with maintaining the required flowmeter run.

Eccentric reducer Steam flowmeter Flow Flowmeter run Fig. System design considerations Adopting a structured approach to steam flowmetering will help to ensure that: o o o o. The design objectives are achieved. No elements of the design are omitted.

The benefits are maximised. The financial outlay is minimised. There are two main elements to such an approach: 1. Consideration of the existing steam supply system The planner should identify any future changes to the plant or process that may affect the installation of steam flowmeters, and should consider whether the installation of flowmeters is likely to act as a catalyst for such changes.

Identifying the aim of installing steam flowmetering Typically, one or more of the following design criteria will be clearly defined: o o o o. To provide information for accounting purposes, such as departmental allocation of costs. To facilitate custody transfer, for example where a central station sells steam to a range of clients. To facilitate Monitoring and Targeting M and T policies and observe trends.

To determine and monitor energy utilisation and efficiency. Each of the above criteria imposes different limitations on the design of the steam flowmetering system. If flowmetering is to be used for accounting purposes or for custody transfer, it will be necessary to install a sufficient number of flowmeters for consumption to be assigned to each of the cost centres.

Also, if the product being sold is energy not steam, flowmeters will also have to be installed on the condensate return lines, as this hot water will have a heat value. For both applications, the highest possible standard of flowmetering will be required, particularly with respect to accuracy, turndown ratio, and repeatability.

The system may also require check flowmetering so that consumption can be proven correct. Embed Size px x x x x Steam has come a long way from its traditional associations with locomotives and the IndustrialRevolution. Steam today is an integral and essential part of modern technology. Without it, ourfood, textile, chemical, medical, power, heating and transport industries could not exist or performas they do.

Steam provides a means of transporting controllable amounts of energy from a central, automatedboiler house, where it can be efficiently and economically generated, to the point of use. Thereforeas steam moves around a plant it can equally be considered to be the transport and provisionof energy. Steam and condensate loop spirax sarco Steam trapping solutions that effectively remove condensate The same steam and condensate system, The water which forms is known as condensate, Steam and Condensate - A basic overview of a steam system the steam and condensate loop What is condensate?

Steam and condensate loop spirax sarco For information about Kestrel Airpark e-mail Gail Digman procedures 've a other download the steam and condensate loop corporation Come to No.

Par cates micheal le lundi, mars 1 , Wednesday, 21 October administrator. Share :. Introduction When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind.

William Thomson Lord Kelvin - Many industrial and commercial businesses have now recognised the value of: o o o. To browse Academia. Skip to main content. By using our site, you agree to our collection of information through the use of cookies. To learn more, view our Privacy Policy. Log In Sign Up.

Steam trapping solutions that effectively remove condensate The same steam and condensate system, The water which forms is known as condensate, Steam and Condensate - A basic overview of a steam system the steam and condensate loop What is condensate? How why should it be recovered? The 3 levels represent: 1. The lowest allowable water level to ensure the bottom of the tank is covered. The highest allowable water level to ensure there is no discharge through the overflow.

The ideal level between 1 and 2. The operator is aiming to maintain the water in the vessel between levels 1 and 2. The water level is called the Controlled condition. The controlled condition is achieved by controlling the flow of water through the valve in the inlet pipe.

The flow is known as the Manipulated Variable, and the valve is referred to as the Controlled Device. The water itself is known as the Control Agent.

By controlling the flow of water into the tank, the level of water in the tank is altered. The change in water level is known as the Controlled Variable. Once the water is in the tank it is known as the Controlled Medium. The level of water trying to be maintained on the visual indicator is known as the Set Value also known as the Set Point. The water level can be maintained at any point between 1 and 2 on the visual indicator and still meet the control parameters such that the bottom of the tank is covered and there is no overflow.

Any value within this range is known as the Desired Value. Assume the level is strictly maintained at any point between 1 and 2. This is the water level at steady state conditions, referred to as the Control Value or Actual Value. Note: With reference to 7 and 8 above, the ideal level of water to be maintained was at point 3. But if the actual level is at any point between 1 and 2, then that is still satisfactory.

If the inlet valve is closed to a new position, the water level will drop and the deviation will change. A sustained deviation is known as Offset. His eye could be thought of as a Sensor. The brain could be thought of as a Controller. It is worth repeating these points in a slightly different way to reinforce Example 5.

Level 3 can be considered to be his target or Set Point. The operator physically manipulates the level by adjusting the inlet valve the control device. Because of this, it is unlikely that the water level will be exactly at Level 3 at all times. Generally, it will be at a point above or below Level 3.