Advanced Control Concepts in Industrial Boiler Control

By Rob Kambach
Senior technical specialist,Invensys Foxboro

Tips for burner modulation, air/fuel cross-limiting, excess-air regulation, oxygen trim, and total heat control Boilers are often the principal steam or hotwater generators in industrial plants or commercial buildings. Consequently, they must be designed to operate efficiently and safely while responding rapidly to demand changes. Burner-management systems must be equally adaptive. Control techniques from several manufacturers are capable of reducing operating costs while providing resources for greater flexibility in plant management and control. Burner combustion control generally includes one or a combination of methods: regulation of excess air, oxygen trim, burner modulation, air/fuel cross-limiting, and total heat control. Be sure when shopping for a control system, these items are included.

Excess-Air Regulation

In actual practice, gas-, oil-, coal-burning, and other systems do not do a perfect job of mixing the fuel and air even under the best achievable conditions. Additionally, complete mixing may be a lengthy process. Figure 1 shows that to ensure complete combustion and reduce heat loss, excess air has to be kept within a suitable range. The regulation of excess air provides:

· A better boiler heat-transfer rate.

· An “advance warning” of flue-gas problems (excess air coming out of the zone of maximum efficiency).

· Substantial savings on fuel.

FIGURE 1. To Ensure complete combustion and reduce heat loss, excess air must be kept within a suitable range

Oxygen Trim

When a measurement of oxygen in the flue gas is available, the combustion control mechanism can be vastly improved (because the percentage of oxygen in flues is closely related to the amount of excess air) by adding an oxygen trim-control module, allowing:

· Tighter control of excess air to oxygen setpoint for better efficiency.

· Faster return to setpoint following disturbances.

· Tighter control over flue emissions.

· Compliance with emissions standards.

· Easy incorporation of carbon monoxide or opacity override.

Burner Modulation

Modulating control is a basic improvement in controlling combustion. A controller monitoring the steam or hot-water line generates a continuous control signal. Reductions in steam pressure or hot-water temperature lead to an increase in firing rate. The advantages of introducing burner modulation in combustion control include:

· Fuel and air requirements are continuously matched to the combustion demand.

· Steam pressure or hot-water temperature is maintained within closer tolerances.

· Better boiler efficiency.

· The weighted average flue-gas temperature is lower.

Air/fuel Cross-Limiting

A cross-limiting combustion-control strategy ensures that there can never be a dangerous ratio of air and fuel within a combustion process. This is implemented by always raising the airflow before allowing the fuel flow to increase, or by lowering the fuel flow before allowing the airflow to drop.

FIGURE 2. Depiction of cross-limitingcombustion circuit. The firing of multiplefuels simultaneously can be accommodated within this scheme.

Figure 2 depicts a simplified control block diagram of the cross-limiting combustion circuit. Combination firing of multiple fuels simultaneously can be easily accommodated within the scheme.

Cross-limiting combustion control is highly effective and can easily provide the following:

· Optimization of fuel consumption.

· Safer operating conditions by reducing the risk of explosion.

· Fast adaptation to variations in fuel and air supplies.

· Satisfaction of the plant steam demand.

Applying additional dynamic limits to air and fuel setpoints can achieve additional savings by having the actual air/fuel ratio maintained within a preset band during and after transition. This protects against having the demand signal driving the air/fuel ratio too lean, therefore reducing heat loss.

Boiler-Drum-Level Control

Boiler-drum-level control includes two-and-three-element-drum-level control and enhanced three-element drum-level control. Boiler-drum-level control is critical for both plant protection and equipment safety and applies equally to high and low levels of water within the boiler drum.

The purpose of the drum-level-controller is to bring the drum up to level at boiler start-up and maintain the level at constant steam load. A dramatic decrease in this level may uncover boiler tubes, allowing them to become overheated and damaged. An increase in this level may interfere with the process of separating moisture from steam within the drum, thus reducing boiler efficiency and carrying moisture into the process or turbine. The three main options available for drumlevel control are:

1. Single-Element Drum-Level Control

This is the simplest but least effective form of drum-level control. This consists of proportional signal or process variable (PV) signal coming from the drum-level transmitter. This signal is compared to a setpoint, and the difference is a deviation value.

This signal is acted upon by the controller which generates corrective action in the form of a proportional output. The output is then passed to the boiler feedwater valve, which then adjusts the level of feedwater flow into the boiler drum.

Some key points to remember when using single-element drum-level control:

· Only one analog input and one analog

· Can only be applied to single boiler/single-feed-pump configurations with relatively stable loads since there is no relationship between drum level and steam or feedwater flow.

· Possible inadequate control option because of the swell effect.

FIGURE 3. Drum-level control with two-element module

FIGURE 4. Drum-level controlwith a single-element module.

FIGURE 5. Drum-level control with athree-element module.

2. Two-element drum-level control.

The two-element drum-level controller can best beapplied to a single drum boiler where the feedwater is at a constant pressure. The two elements are made up of the following:

· Level element, a proportional signal or PV coming from the drum transmitter. This signal is compared to a setpoint, and the result is a deviation value. This signal is acted upon by the controller, which generates corrective action in the form of a proportional value.

· Steam-flow element, a mass-flow rate signal (corrected for density) is used to control the feedwater flow, giving immediate corrections to feedwater demand in response to load changes. The level controller corrects any inbalance between steam mass flow out and feedwater mass flow into the drum. This imbalance can arise from:
- Blowdown variations caused by changes in dissolved solids.
- Variations in feedwater supply pressure.
- Leaks in the steam circuit.

Some key points to remember when using two-element drum level control:

· There is tighter control of the drum level than with only one element.

· Steam flow acts as a feed-forward signal to allow faster level adjustments.

· Can best be applied to singleboiler/single-feed-pump configurations with a constant feedwater pressure.

3. Three-Element Drum-Level Control

The three-element drum-level control is ideally suited where a boiler plant consists of multiple boilers and multiple feedwater pumps or where the feedwater has variations in pressure or flow. The three elements of this system are the level, steam, and feedwater-flow elements.

The level and steam elements team correct for unmeasured disturbances within the system such as:

· Boiler blowdown.

· Boiler and superheater tube leaks.

The feedwater-flow elements responds rapidly to variations in feedwater demand, either from the:

· Steam-flow-rate feed-forward signal.

· Feedwater pressure or flow fluctuations.

To achieve optimum control, both steam and feedwater flow values should be corrected for density. Some key points to remember when using three-element drum-level control:

· This system provides tighter control for drum level with fluctuating steam loads. It is ideal where a system suffers from fluctuating feedwater pressure or flow.

· A more sophisticated level of control required.

· Additional input for feedwater flow is required.

FIGURE 6. With demand sharing, the firing rate of the modulating boiler increases until the load requires an additional boiler. At this point,the additional boiler is started and becomes the modulating boiler.

To level control over wide ranges of steam demand, the three-element mode is used during high steam demand. The two-element mode is used if the steam-flow measurement fails and the module falls back to single-element level control if the feedwater-flow measurement should fail or if there is a low steam demand.

Demand-Load Scheduling

One of the primary goals in operating a boiler plant is to ensure that the working steam pressure (or temperature in hot-water systems) is sustainable for any load demand placed on the plant. At the same time, this requirement must be met as efficiently and cost effectively as possible. Some valuable features of demandload scheduling are:

· Operator selection of baseload or modulating operation.

· Parallel or serial demand sharing.

· Boiler banking.

· Eight-day timer.

· Multi-sequence program selection.

In a multi-boiler plant, this can be achieved through the implementation of demand-load management, the purpose of which is to distribute the steam demand in an optimized manner and to adjust the boiler-plant output to meet working requirements. This ensures that boilers are fired only when required, thus reducing running costs. Alternatively, demandload management can allow each boiler to be allocated the same amount of running time.

Demand-load management should offer the following:

· The demand share arrangement allows each boiler to be operated in either base-load or modulating service. This allows to system to utilize the best distribution of load between the boilers and result in the lowest overall cost. The base-load operation leaves the implementation up to the operator. In this mode, the total demand is shared between the base-load boilers in proportion to the operator-set base-load values. The modulating mode of operation, on the other hand, enforces automatically the load allocation without the need for operator intervention. The total demand, less that satisfied by the base-load boilers, is shared between the modulating boilers in proportion to their capacities. The flexibility of the control module is such that one combination of boiler modes can be applied dynamically to the boiler plant.

· Effective load allocation is based on real-time calculations taking into account operating safety margins, load fluctuations, required shut-down characteristics, and boiler capacities.

· Demand-sharing methodology may also be implemented – in parallel or series – depending on plant requirements. In parallel, the available boilers share the total demand simultaneously by taking up an equal firing rate to meet the load. On load increase, the firing rate of all modulating boilers will increase equally until the load requires an additional boiler. At this point, the firing rate of the active boilers decreases to compensate for the firing rate of the newly started boiler. Figure 6 illustrates the process for an increase in load.

· Parallel modulation is generally implemented for steam boilers. It offers the most effective control when relatively steady process loads are available. As the system modulates the boiler plant to adjust the common header pressure to the required setpoint, a smoother response to changing load conditions is performed by the controller.

· Series demand sharing allocates loads by normally forcing one boiler at a time to modulate to satisfy the demand. On load increase, the firing rate of the modulating boiler will increase until the load requires an additional boiler. At this point, a new boiler is started and becomes the modulating boiler. The other active boilers are ramped to their optimum firing rate.

Series modulation is generally implemented for hot-water systems or fluctuating steam loads. This mode allows faster individual boiler response to plant conditions as the boiler pressure is adjusted to the required setpoint. The boilers that are chosen to always run are referred to as the “lead” boilers. All the other boilers are “lag” boilers but are prioritized so that a boiler with a high priority always runs before a boiler with a low priority and so on (i.e., the most effective boiler is always started first, and the least effective one is always stopped first).

Boiler banking keeps the available boilers in hot standby mode until required to fire. This is achieved by intermittently firing the unused boilers, thus maintaining a required pressure by use of upper and lower banking thresholds or by recirculating the return water through the boilers to keep them hot. The main advantage of boiler banking is that it acts as a “warm”-start facility, improving the plant response to sudden load changes.

Remember that demand-load management is an optimizing function that augments, but does not replace, the combustion-control system.

Conclusion

Taken together, burner modulation, air/fuel cross-limiting, excess-air regulation, oxygen trim, and total heat control, can provide excellent control and fuel efficiency for most boiler systems.

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Go Green!!!

Top Environmental Issues

The world cannot go a day without having new problems. Disasters, social issues and pandemics are only a few of them. But what continues to haunt humans daily is the fact that the environment is slowly deteriorating everyday. Environmental issues cloud over the hope and future of generations to come. Although efforts have been made they don’t seem to be enough. Here are the issues that top the heart-breaking list:

§ Climate change – Global warming is as popular as a box-office hit movie. It’s because it’s a clear shot of every human being’s abuse to the environment. And the ripple effect of climate change is so massive that practically everything is affected. It has brought about more storms, more deadly diseases, extreme weather, earthly disasters such as floods and heat waves, and it has also brought about plant and animal extinction.

§ Overpopulation – It cannot be denied that there is a link between overpopulation and poverty. Poor countries become poorer and the gap between the privileged and those suffering from paucity has gotten bigger. Many have become promiscuous but refuse to practice safe sex or lobby for reproductive health in fear of going against church beliefs.

§ Big oil vs. renewable energy – While there’s an abundant source of renewable energy from the sun, the wind and the earth, many still produce energy from fossil fuels because big oil companies seem to dominate the economy. So there are those who refuse to subsidize research and harvesting of renewable energy from natural sources. Energy production from fossil fuel continues to cause harmful gas emissions that lead to global warming.

§ Endangered species – Many plants and animals are threatened to extinction because of climate change and aquatic and land mass abuse. The African elephant, the bald eagle and the golden toad are only a few of what we might not be able to see anymore in the years to come. Species extinction can badly affect the food chain and the whole environment itself.

Green It and Love It

Does being a green home owner have an appealing ring to it? Whether you’re thinking of having an old kitchen or bedroom renovated or planning to build a healthy home, there’s one advice from modern-day architects and contractors you won’t regret: “green it!”

If you’re tearing things apart in your existing home, take the opportunity to identify pre-existing toxicity problems. A certified indoor air quality inspector may be of help to you in this aspect. When you’ve looked at the blueprint for your healthy home and you’re determined to proceed and green it, one of the things you also need to do is to collate a list of suppliers and home improvement stores which can provide many environmentally friendly products like non-toxic paints. Do you feel like you lack the resources or expertise to make well-informed choices leading to the building of your healthy home? Check out websites, or get recommendations from architect-friends.

For your kitchen or bathroom, don’t forget to have a vent installed to pull in fresh air from the outside. Prioritize cross ventilation so you can enjoy natural heat and cooling as much as you can. For your cabinets and shelves, find less toxic materials. Products made from bamboo are worthy options. Thinking about carpeting? Carpets easily collect dust mites and dander, impeding easy breathing. Better alternatives are bamboo flooring, cork or hardwood with a throw rug made of natural fibers.

When construction of your home is completed, take additional steps to constantly green it by using eco-friendly cleaning products. Replace appliances that don’t run efficiently. The wrong refrigerator, tv, or microwave oven may not make you sick, but those that consume much energy contribute to air pollution and global climate change.

Simple Tips on How to Go Green

Going green is a phrase you hear more often these days. It’s because people have finally come to realize that they should help save the environment in their own little ways instead of waiting for the government or environmental groups to do everything. Some don’t realize that it’s a person’s over-all lifestyle and daily demands that have piled up to all the inhuman practices which cause global warming. Yes, there are natural phenomena, but most environmental issues and disasters are still human-induced. So how do you start going green? Here are 3 useful tips that will help cut back on carbon emissions, save more money, and also restore your health.

§ Cut back on energy consumption- It is wise to do outdoor activities again instead of staying on the couch all day and watching TV or fiddling with your computer. You get to save a lot of energy and also reduce your risk of obesity. Always turn off appliance and unplug them when not in use. You’ll save about 30% of energy in a year. And continue to upgrade them. Change your light bulbs to smart energy-saving bulbs. They give more light and consume less energy. And use lap top computers instead of PC’s. Believe it or not they consume 90% less energy if you maximize the battery.

§ Take a walk and eat smart – Walk to work or to any short distance destination. You’ll cut back on around 8,000 pounds of carbon emission annually if you let your car rest more often. Walking won’t hurt you and will better your cardiovascular health. Also, take organic food and eat low on the food chain. Have as many meatless days possible.

§ Save water and counter global warming – Shower for shorter periods of time and use low-flow showerheads to save water. Have drought-tolerant plants in the garden so you don’t have to water them all the time, and don’t forget to plant a tree. If global warming seems hard to runaway from, then to something to counter it gradually. A tree eats up carbon dioxide and releases oxygen during photosynthesis. Planting a tree is like installing a lifetime air cleaner.

Green Living Tips for Today’s Young People

In today’s ecologically conscious world, many smart young people are heeding the green living tips offered by parents and older peers. The benefits are clear. Eco-friendly products translate to huge cost savings and minimize harm to the environment.

So how do today’s young people show they care for the environment? Let’s start with modern commuting trends. If you’re college-bound kid is not the lucky recipient of an environmentally friendly car (as a graduation or birthday gift), then chances are, he/she may be taking public transportation (which is good) or driving the traditional car. Don’t look now but ingenious minds have devised an online social rideshare and carpool matching system that uses a popular social networking site to hook riders up with drivers en route to a common destination.

For the young ladies in the family who love to shop, green living tips they may have gravitated to include bringing their own eco tote bag so as not to amass more plastic bags than can be reused at home. In so doing, young gals (and their shopaholic moms, too) get to save lots of trees and keep plastic bags out of landfills.

Young ones also contribute to resource conversation by keeping in mind other green living tips like taking quick showers, buying and using products – like organic cosmetics -- that do not contain synthetic substances, as well as clothes and accessories made of organic cotton or hemp. Switching off room lights and computer equipment (including the monitor) when not in use and going for green food options are likewise some of the ways to lessen the eco footprint.

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Thermal Cleaning of Heat Exchangers

Cleaning of heat exchangers polluted with (partly) organic contaminations like cokes, plastic, oil, paint, rubber, food etc. still is a major problem for many companies. The need of parts’ cleaning is found in each and every industrial branch. Some take it as a daily necessity; others consider it an incidental procedure in times of calamity, turnaround or shutdown. Apparently it is just part of the game, but nevertheless it should be done as quickly as possible and as best one can. In most cases this is very often related to the available knowledge of the known cleaning techniques.

Photo 1: Heat exchanger soiled with plastics

As a result of the ever increasing quality of final products, the search for longer running times, the need for better cleaning results and cutting down costs or due to more stringent environmental laws and procedures, most of the traditional methods of cleaning, like chemical or high-pressure cleaning, are sometimes no longer adequate. Maybe the thermal cleaning method can offer the desired solution for your cleaning problem?

Thermal cleaning methods

1. Advantages of thermal cleaning

Vaporizing organic elements only yields some 5 to 10% of the original pollution, which can be easily removed. Moreover, thermal cleaning very intensively removes the broadest range of pollutants in a relatively short period of time, without causing damage to the substrate.

2. Brief introduction to the technique

2.1. The process

Pyrolysis is the thermal conversion of organic materials in an oxygen-poor environment. At a temperature below 400°C (750°F) the organic materials are converted into a homogeneous residue, ready for further controlled processing.

At such high temperatures higher hydrocarbons are decomposed into components with a much lower molecular mass, resulting in pyrolysis gases (ethane, ethene, propane, propylene), pyrolysis oil which contains aromatic components and a carbon-rich residue.

The pyrolysis gas as well as the oil is transformed into carbon dioxide and vapour, because of partial oxidation. This phase is exothermic, at which 40% of the released energy is re-used to decompose the organic material.

A very important factor in the process, together with a steady heating and cooling, is maintaining a constant temperature, in order to prevent damage to the parts that are to be cleaned. This is also important in order to avoid unwanted (waste) gaseous fractions.

3. Pyrolysis ovens

As stated before, this is the only correct thermal cleaning technique for the treatment ofsoiled heat exchangers. To give you of proper idea, I will describe the general functioning of this type of installation, after which the conditions necessary to guarantee a safe and perfect heat exchanger cleaning will be further examined.

General functioning

The pyrolysis ovens consist of an operating room of 1 to 75 m³, depending on the type. The common maximum dimensions currently are 8m x 3m x 2,5m, but note that even bigger dimensions are also possible.

The objects to be processed are put on a loading cart, which is pulled into the furnace chamber. After closing the door, this chamber is made inert by lowering the oxygen level to 8%. Then the temperature is slowly increased to 420°C (788°F), depending on the character of the objects and the kind and amount of pollution.

The oxygen content of the cheapest oven systems is even not controlled. It is taken for granted that the oxygen will leave the chamber automatically during the gasification. If the temperature increases after all, a lot of water is injected so that the temperature has to fall. These are of course the real paint stripping ovens which are note suitable for the “real” job.

When the temperature required for vaporizing is reached, a slight overpressure leads the released gases towards the afterburner chamber. Here they are processed at high temperature, after which they are removed. Occasionally this air current is used for heat recycling in order to recover a part of the energy.

As a result of the fact that all organic components are gasified because of the heat, only a residue consisting of pigments and inorganic fillers remains after cooling. This is in general 5% of the original pollution volume and can be easily removed by various techniques.

Because the heat is able to reach every spot – also in the middle of tube heat exchangers or between the tubes and the shell of a heat exchanger with fixed shell -thermal cleaning is extremely suitable for heat exchangers. This is impossible with for example only high-pressure cleaning.

Special conditions for the thermal cleaning of heat exchangers

To be sure that the heat exchanger gets the best possible thermal treatment, a number of essential matters have to be respected. Besides a proper oxygen control, there exists a method to monitor the exchanger itself by means of thermocouples at various with the owner agreed spots. It is important to utilize object temperatures instead of chamber temperatures in order to be able to follow the process in the oven correctly.

Another important technical aspect is the presence of an excellent internal circulation unit which takes care of a proper circulation in the oven chamber. Due to this there is a homogeneous temperature on all sides which is essential to avoid temperature differences inside the object to clean.

The newest systems dispose of an internal heat exchanger to cool down with air instead of water. Through this, temperature control has increased considerably; it is almost made possible to steer accurate to a degree. Moreover not having to inject water in the chamber involves less trouble with volatile rust on the parts to clean.

To draw up a proper temperature protocol, it is important to know the exact composition of the material as well as the pollution. In case of doubt, a reliable laboratory analysiscan give a decisive answer. The weight of the exchanger, the type of material, the geometry and the type of pollution determine the heating up and cooling down curve and can largely give an indication of the total necessary time in the oven.

Photo 12: After thermal cleaning, note that also the paint will be gone afterwards

Also the pollution itself strongly influences the temperature program to follow. Does the pollution liquefies before it gasifies - like some plastics - or does it remains solid until complete gasification? A laboratory analysis or practical research can also give a decisive answer on this matter, which enables a more correct assessment of the program.

If the pollution liquefies during the heating up, there will be a foreseen phase in the program around the melting point of the pollution. This phase enables the pollution to melt in large measure out of the object to clean. Subsequently the gasification of the remainders can more easily take place and the total cleaning time will be reduced. In case of extreme pollutions of thousands of kilos, even a two-phase treatment can be chosen. A great part of the pollution will than be melted during a first thermal treatment at low temperature. Afterwards the remaining part will be gasified completely during a second treatment to remove the pollution entirely.

Also the type of material used for the construction of the heat exchanger is very important; after all the material determines the maximum temperature for the thermal treatment. Although there are differing opinions concerning the possible thermal cleaning of duplex steel bundles, various tests have revealed that this type of heat exchangers can be properly cleaned using this method. Only the maximum delta T between the different thermocouples is much lower than with exchangers made out of regular steel types, due to the expansion differences between the metals used in duplex steel.

Besides all conditions concerning the correct installation technique, a proper knowledge of the used material and an analysis of the pollution, also the know-how of the oven operator is very important. The operator has to know exactly which program to follow in order to have the correct heating up and cooling down process. During the thermal cleaning of a heat exchanger, it is imminent that the material is heated up and cooled down simultaneously to avoid internal tensions. The operator has to make sure that the temperature is steered in such a way that it increases or decreases at the same time on the inside as well as on the outside. This can be done in large measure automatically by means of thermocouple steering in the newest installations, although supervision is still necessary.

Advantages of thermal cleaning for the different types of heat exchangers

The traditional methods for the cleaning of heat exchangers are often very effective and therefore used for many years. Nevertheless there are a number of very specific problems which everyone recognizes. The problem with high-pressure cleaning is the deterioration of the surface as well as the accessibility of the pollution. Remainders involve that your exchanger has to be taken out of production sooner to be cleaned again.

Using chemical cleaning can sometimes take a long time to dissolve the pollution. The availability of the bundle will be postponed. Thermal cleaning on the other hand is very effective and reaches every spot. The results proof that a degree of cleanliness of almost 100% can be reached which results in longer operating times and consequently cost savings.

To be quoted as a good example are the heat exchangers from a naphta cracker which were cleaned with high-pressure every two months. After the first thermal cleaning, they could be used without problems during 2 years; a huge improvement. And there are more.

Hereunder you will find a definitely not complete overview of the different types of heat exchangers, together with the typical advantages and disadvantages of thermal cleaning for each.

Pipe bundles

· With this type of heat exchanger, the contamination can be in or/and around the tubes. High-pressure cleaning has the problem that the water jet can barely reach the very inside of the exchanger to remove the pollution around the tubes. This means that some bits are left behind so the contamination happens more quickly during the production, resulting in a shorter operating time.

· Thermal cleaning destroys the pollution everywhere and therefore gives a much better level of cleanliness which results in a longer operating time. For extreme contamination, often a high-pressure cleaning is used for the first rough cleaning of the bundle, after which thermal cleaning can take place.

· In case of hairpin bundles, thermal cleaning can remove the pollution inside the corners of the tubes easily, where most of the times the problems occur.

Bundles with a fixed shell

· The problem with classic high-pressure cleaning is that there is practically no access to do a cleaning around the tubes. Often chemical cleaning by flushing is used to clean the soiled inside, but the effectiveness is often very poor. Very good results were seen using the thermal cleaning method to remove the pollution around the tubes.

· To get a good temperature control on the inside of the heat exchanger often a blow through system is used to allow a good air ventilation on the inside of the shell. Besides of the heat, you will need a bit of oxygen to get a good oxidation of the pollution. Otherwise you will be confronted with carbonized material after the thermal treatment which is very difficult to remove.

· Like always all organic parts are reduced to ashes, but in this case it is better to use air to remove already a great part of this dust. Using water will leave the remaining ashes very sticky and therefore difficult to remove all of it. After the cleaning by air, a rinsing with water is done, but there still can be the possibility that during the first running hours, dust particles coming from remaining ashes can disturb your process. This normally goes away after a short time. In some cases an endoscopy is done to verify the result of the cleaning on the inside.

Bundles with static mixers (fix or non-fix)

· High-pressure water cleaning has no use here, the penetration degree is zero. Chemical treatment can give results depending on the possibility of a flow on the inside of the used chemical to dilute the pollution enabling it to be removed. In most cases however both traditional methods gave a very poor result, which immediately shows the necessity of the thermal cleaning method.

· First the thermal treatment will be executed to destroy the organic pollution on the inside of the static mixers. Then a combination of water and air is used to remove the dust particles from the inside of the mixers. This is done until the water is clear again, which indicates that most of the ashes are gone.

· No guarantee can be given after the treatment that it is 100% clean, because in case of the use of fix static mixers, no control method can be used to inspect the inside of the tubes. The only control you will have is to see that the water flows trough normally, so the tube is not blocked.

· After the cleaning procedure is done, there also might be the possibility of dust particles in your flow during the first running hours. This is not the case with removable static mixers, because they are removed after the thermal treatment and worked on separately to get them 100% clean.

Spiral or plate heat exchanger

High-pressure does not give an optimal result here either, and chemical cleaning generates an awful lot of waste. With the classic methods, there are always deposits left on the walls, which means the exchangers become dirty more quickly during production; that's why thermal cleaning is also the most feasible solution here.

Compablocs

· Traditional water cleaning is, depending on the pollution, in some cases very difficult even impossible.
Like with all other heat exchangers, thermal cleaning offers a good possibility to make your Compabloc almost new again using controlled heat and a good rinsing afterwards.

Twisted tube heat exchangers

· Because of the twist in the tubes, the accessibility needed for a good cleaning by water is very poor. You only can clean the outside like this.

· Thermal cleaning offers very good results because of its technical characteristics. All dirt will be removed also from the very inside of this kind of heat exchangers.

Plate heat exchangers

· In most of the cases a chemical treatment is used and has been proven to be very effective to clean the soiled plates of this kind of heat exchangers. High-pressure cleaning is sometimes done, but the risk of damaging is very high.

· Thermal cleaning can be used to remove all kinds of pollution on the plates, like glue, and a polymerized or carbonized pollution, which are difficult to remove with chemicals.

· Thermal cleaning however can not remove scale, while this is inorganic!

Certainly more types of products can be cleaned with the thermal cleaning method like big vessels, pumps, extruder parts, filters, pipelines, reaction vessels and many more. Also all kinds of organic pollution like PP, PE, PS, PC, SAN, PET, PA (also reinforced), PBT, PU, carbonized material, cokes etc. can be removed, which shows that the thermal cleaning method has a very high potential as a substitute or even an improvement for today’s cleaning techniques. In fact in a lot of cases, the thermal cleaning technique offers you the possibility to make your soiled heat exchangers or other parts like new again. This surely is an advantage which can not be ignored. Therefore I hope the information given to you in this article helps you to make the right decision next time a cleaning problem occurs.

For more information, please contact Robert Mol (robert.mol@thermoclean.com)

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