Designing An Optimal Heat Exchanger from The Quran

If you think that the heat exchanger text book, software and experience is the only reference for you to design an optimal heat exchanger and heat exchanger tubing, then we should look at this interesting video. It shows in detail and provide valuable message on the ultimate optimal heat exchange design. Check it out:






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Better Heat Exchanger Cleaning Through Technology

Maintenance of a platform's Waste Heat Recovery Unit (WHRU) and similar shell and tube heat exchangers can be an extremely dangerous process. It needs to be disconnected, taken off line, and moved to shore for repair. Shell and tube heat exchangers are made of coiled tubes and can become fouled with carbon deposits. The traditional methods for clearing the blockage include bypassing the fouled unit, cutting off bends and cleaning the tubes, then re-welding the U-bends, and complete unit replacement.

The old methods are becoming more outmoded due to advancements in technology. It is inefficient to bypass the unit. Just as it would be less efficient to run your car with 2 cylinders not firing. This inefficiency, of course, also increases operational costs. It is time consuming and costly to cut the U-bends and re-weld them. Sometimes it can be difficult or impossible to get access to reattach them.

Some of these new methods include the ability to clean areas with limited access, and clear deposits from U-bends without ever removing them. This can sometimes be done without even taking the unit offline, and usually takes less time and results in a higher degree of defouling. In fact, many units can be restored to near-factory efficiency. For big refineries, petro-chemical plants, or power plants, this can amount to six figure savings.

The U-bends themselves also retain many deposits, and continue to be a bottleneck to the system. Full replacement carries the cost of completely replacing equipment that, other than the heat exchanger tube fouling, is still in working order. This method also requires the unit be taken offline for the full duration of replacement. obviously this carries a heavy expense and serious loss of production.

Traditional heat exchanger cleaning methods and heat exchanger cleaning equipment have changed very little over the last few decades. Pressure jetting is still the primary means used by many companies, but it is slow, inefficient, and ultimately very costly. Additionally, many companies are skeptical of newer methods, falling back on the "that's the way it's always been done," chain of logic. They are also weary of trying new techniques that are not as "proven" to be effective. Finally, many have long term tube cleaning contracts that do not allow for a change in heat exchanger cleaning technique, unless the contractor were to adopt the new methods.

Newer heat exchanger cleaning equipment and techniques are more technologically advanced, and by extension, require a higher skilled laborer than old style pressure jetting. These new developments include the ability to clean tight radius bends, clean units while keeping them in place, and even while keeping them online. It has also resulted in faster, more efficient cleaning. Many tube bundles can now be cleaned more effectively than with pressure jetting, and jobs that used to take days may now take only a few hours. Difficult to access units are now accessible with these new technologies.

Some of the technology that has been developed includes special nozzles that can be used on tight bends, laser cleaning, and new "smart" metals that respond to changes in density and pressure to prevent damage to the tubes. With these methods, jobs can be finished with less downtime, because cleaning and descaling can be done more quickly. Equipment is also less likely to be damaged in the process. Many of these new processes are safer, create less waste, use no chemicals, and have a significantly reduced environmental impact.

The article was written by Alex Parry who writes about heat exchanger safety at his heat exchanger cleaning equipment site.

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Cleaning Plate Heat Exchanger Matter

I made a post entitled "Learning Process From Cleaning Plate Heat Exchanger" which was a follow up entry from "Some Updates". You can refer to the 2 posts for reference. From that post, I received some interesting response and questions from few engineers asking more detail about the cleaning of heat exchangers. The questions are taken from the comment section of that Learning Process From Cleaning Plate Heat Exchanger post without any editing. I answered the questions but I add more of my answers here after thinking about it...

Questions:

I'm a process engineer and your article is very useful and interesting. Could you say (if it possible) how long time did this plate heat exchanger work good without cleaning? And was the concentration of caustic solution high?

Answer:

Thanks for your kind words Olga.

How long time did this plate heat exchanger work good without cleaning?

That depends on how you use the plate heat exchanger and the types and quality of fluid that passes the plate heat exchanger. From my experiences, the plate heat exchanger can operate effectively up to 1.5 years without cleaning, but that is because the feed oil is clean and other combining parameters are good. There are also cases where we have to clean the heat exchanger after 4-5 months... There's no straight answer to this. It depends on a lot of factors. You need to really sit down and monitor the processing parameters and the quality / condition of fluid entering it. I have about 16 plate heat exchangers which I monitored and all of them have different records. Those who belong at the same section in the plant will have almost similar cleaning track record. All of them have different classification of problems too. So, we need to really look at the heat exchanger(s) and make a proper inspection, evaluation and analysis.

The caustic concentration was 3-5%. This also depends on how severe the scale build up is inside the plates. You can have lower concentration if the scale is lesser. You can add up more of the caustic concentration, but it may be not good for your plates (of the plate heat exchanger) or the tubes (of the shell and tube heat exchanger).

Questions:

How heavy and fooling is that oil?

Does it really worth the trouble to use a plate exchanger respect to a shell and tube for such fluids? After all a shell and tube is much easier to clean.

Answer:

It depends on your process and application. What is the type of flow? what is the pressure and temperature? You have to use a shell and tube heat exchanger if you have a high pressure and high temperature. A shell and tube heat exchanger is more expensive. A plate heat exchanger is cheaper and can be used for lower temperature and lower pressure. The main constraint of the plate heat exchanger is because of the gasket used cannot cope with temperature higher then 200oC. so, it's a matter of the effect of process parameters and not the easiness to clean the heat exchanger. A shell and tube heat exchanger 2 pass (or U tube) is also sometimes very difficult to clear especially at the U bend. You need a special equipment with high pressure of jet water to clear the scale, fouling. In worse cases, you need to introduce a small drill combined with the high jet water, preferably up to 20,000 psi to ensure you eliminate the stubborn scale.

Hmmm...maybe those of you who have other experiences on dealing with heat exchanger cleaning can share it with us here...TQ!

The author of this post is Zaki from Chemical Engineering World - subscribe to the blog...
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Furnace Flue Heat Exchanger - Economizer

This is an interesting video about how to make full use of the energy from a heat source. In this case it is a furnace and it acts as an economizer. The video shows how waste heat from the furnace is used to pre-heat the hot water tank feed reducing the amount of energy required and the GHG emissions released. Check it out...

Heat Exchangers for Outdoor Corn Boilers

A heat exchanger is a device designed to efficiently transfer the heat from one medium to another. In the case of an outdoor corn boiler, these media would be air and water.

A typical domestic setup would include a water-to-water heat exchanger for hot water and a water-to-air heat exchanger for forced air home heat. Water-to-water heat exchangers are also used to heat hot tubs, swimming pools and the water for radiant baseboard or radiant in floor
heating systems.

Water-to-Water Heat Exchangers

The three most common types of water-to-water heat exchangers used with outdoor
corn boilers are: Sidearm, Shell and Tube, and Brazed Plate. What differentiates these heat exchangers, besides the cost, is the way they're designed to transfer heat from one medium to another and the method used to create turbulence.

A key component in the efficient transfer of heat between liquids is turbulence. The more turbulent the flow of water through a heat exchanger, the more efficiently heat is transferred.

Sidearm Heat Exchanger

The sidearm heat exchanger is a popular and inexpensive choice for heating domestic hot water. It incorporates a pipe within a pipe design where the water in the inner pipe (your hot water) is heated by hot water from the boiler circulating through the outside pipe.

Turbulence is created by scrolling on the outer surface of the inside pipe.

This straightforward design prevents clogging by sediment and resists scaling. One drawback of the sidearm heat exchanger is reported slow recovery under heavy use. Cost: $130-$150.

Shell and Tube Heat Exchanger

Shell and tube heat exchangers are available in dozens of tube configurations and sizes ranging from a few feet long to 50 feet or more for power plant steam generation.

A variation on the shell and tube design is shell and coil where a helical (spiralling) coil
replaces the tubes.

No matter what the design or application, the basic principle is the same. The water to
be heated flows through tubes, and the heated boiler water, encased by the shell, flows around the tubes.

Turbulence is created by the baffles holding the tubes together in what is called a tube bundle.

Shell and tube heat exchangers for non-chlorinated water applications, such as domestic hot water and hydronic heating, are usually constructed with a brass shell and copper tubes.

For swimming pools and spas the shell should be PVC or stainless steel with stainless
steel tubes. 316L grade stainless steel is commonly used for this application.

Cost: $200-$600 depending on copper or stainless construction and the overall size based on the volume of water to be heated.

Brazed Plate Heat Exchanger

The brazed plate heat exchanger combines compact size with a highly efficient design to produce a device for heat transfer that is up to six times smaller than a shell and tube heat exchanger of similar capacity.

The key to this efficiency lies in their unique construction. Corrugated stainless steel plates are brazed together (eliminates gaskets) with every second plate turned 180 degrees. This design creates two highly turbulent fluid channels that flow in opposite directions (counter flow)
over a massive surface area.

Cost: $100-$500 depending on capacity.

Get better outdoor corn boiler information at Alternative-Heating-Info.com