11 replies to this topic

[kybele39]

Dear All,

When we look at industrial heating based companies, we see steam boilers, hot water boiler etc. sells more comparing the thermal fluid heaters.Because of the below reason thermal fluid heaters seems to me used in the industries:

• Under the atmospheric pressure they can be design for the high temperatures, up to 325-350degree centigrade, even 400degree centigrade.
• They can be designed for customers requested temperature for supply temperature,
• No need any treatment system for the oil like we do for the boiler feed water conditioning,
• No heat loss due to the hot condensate we have in the steam heated systems,
• Low maintenance cost with a smaller dimensions comparing the steam boilers,
• No corrosion worry,
• No need for the certified boiler staff for operation.

For the steam and hot water boilers I can do the same comparison for the topic as below:

• The system cannot designed for the high pressure, high temperature conditions because of the high cost,
• High maintenance cost,
• Corrosion issues,
• Boiler feed water treatment system needed,
• 24/7 boiler operator needed,
• Low efficiency results 80-85% versus to 91-92 % thermal fluid heaters efficiency,

My question is why the thermal fluid heaters sells less than the steam operated boilers if the above benefits are right for each heater style?

When you look at various companies references they are full with steam systems and thermal fluid heaters really rare...IS the design of TFH system is really difficult or what is the real reason customers buys steam operated system?

I need your valuable inputs.

In advance I thank you very much.

Kybele

Edited by kybele39, 30 August 2010 - 09:11 AM.

[Zauberberg]

There are a few reasons I can think of:

1. Having steam system allows you to have multiple temperature levels for heating purposes (reboilers, heaters, heat tracing etc.), depending on the steam pressure which is easily manipulated through e.g. letdown system;

2. Steam is a multi-purpose fluid, as opposed to thermal oil. You can use steam as ejector motive fluid, turbine motive fluid, and certainly you cannot replace it with thermal oil;

3. Quite frequently it is used as live stripping medium in different columns (sour water strippers);

4. Sometimes you don't have choice, and you have to opt for a thermal oil system which is the case in deserts and remote locations with no water sources, or where the costs of treating water and producing steam greatly overweight the costs of a thermal oil system;

As you can see, the choice is not always straightforward. Not only the cost accounts, but also the availability, flexibility, and forms of use of heat energy. I believe there are other reasons as well, and perhaps other forum members can give us their thoughts on the subject.

Best regards,

[ankur2061]

No heat loss due to the hot condensate we have in the steam heated systems,
No corrosion worry,
No need for the certified boiler staff for operation.

Kybele,

The above characteristics for TFH are not exactly true.

Any hot system will have heat loss to the surroundings and this cannot be completely mitigated, only minimized by proper insulation of the TFH and it's connected piping / systems. In fact, the higher the temperature gradient between the hot system and the surroundings higher will be the heat loss.

Corrosion does occur in TFH systems. Due to thermal degradation of thermic fluid, degradation products such as water and carbon dioxide can form which can lead to corrosion of the TFH system. Side-stream filtration and periodic make-up are regularly practiced to keep the corrosion products in TFH under check.

As for any fired heater system including steam boilers and TFH's well trained personnel are always required for operations considering the inherent danger of fire and explosion associated with any fired equipment.

Now to come to the basic question why steam is preferred for heat transfer over thermic fluid and that is simply because the heat available (Btu or KJ) per unit mass (pound or kg) from steam is much higher than that obtained from thermic fluid. However in chemical process industries where high temperatures are required and usage of steam requires very high pressure systems, thermic fluid systems are preferred.

In integrated refining and petrochemical complexes where high pressure steam is required for other applications (turbines, power generation), low presssure steam is produced by pressure letdown of HP steam and utilized for process heating in reboilers and other heat exchange equipment. This is the reason that you find greater application of steam systems compared to thermic fluid.

Hope this helps.

Regards,
Ankur.

[Art Montemayor]

Kybele,

Both Zauberberg and Ankur have, as usual, covered and responded to your query with specific and valuable input. Allow me to add the following to your basic question:

• Water is universally available; it is conveniently furnished worldwide and doesn't require special handling and storage - or pre-invested inventory;
• Water is the universal non-toxic fluid. Unless tainted or contaminated, water is not a health or hazardous threat to humans.
• Lastly, water is a day-to-day, familiar substance that humans are "comfortable" with. Contrary to our knowledge, it is not classified as a "chemical" by the average layperson or news media. Consequently, it has a benign and acceptable effect on most people - as opposed to the complex chemical composition of most thermal heating fluids. This may only be a psychological effect, but it tends to be a strong attraction to water.

I am also biased towards using water as a heating fluid or vapor whereever/whenever I can justify it.

[kybele39]

Dear All,

As always I get very valuable inputs from cheresources's forums. Such a great, knowledgeable community we have here. I appreciate all your responses.

Your responses make sense totally.

Only I thought because of usage of N2 blanket system in the TFH system will decrease corrosion rate quite a bit for the life of the equipment. For this reason I thought no corrosion issue can be seen in the TFH's.

I am also interested in the statistical data if there is any. So far I cannot find this data which shows industries in detail and usage of heating systems and their capacities country by country. I often checked below websites but cant find any data about the process heating in details.

http://www.eia.gov/

Again Thank you very much for all answers above.

Kybele

[Zauberberg]

I believe that many of the forum members can confirm - based on their personal experience - that steam systems (as compared to thermal oil systems) comprise more than 99% of all the systems installed worldwide, which includes refineries, petrochemical complexes, gas plants (if not located in desert or very remote areas, as we discussed above) - and all those listed are great energy consumers.

Some very sound arguments for using steam system, whenever technically and economically feasible, have been presented in this thread. Maybe a few of forum members might say that 99% figure is way too high, but even if it isn't 99% it is certainly in the same ball park.

I'm not sure if you can find this statistical information anywhere in the form of a report, but it would be nice to see it.

[djack77494]

i think that steam or hot water are the "default" heating media; you'll always use one or the other unless there are strong reasons for not doing so. Having said that, there sometimes ARE strong reasons for not doing so. In my mind, however, that roughly 1000 btu/lb of latent heat that can be transferred by condensing steam makes it very hard to beat. Add that the the price of the heat transfer medium (water vs. HT Oil) and any other choice starts with a huge disadvantage. Steam and water are essentially as non-corrosive as the economics dictate. Carbon steel MOC is used for both. Corrosion inhibitors are readily available and reasonably priced. Even though 99% might be a bit high, I'm sure it's not totally off-base.

[kybele39]

Thank you All for your inputs. They've been greatly helpful. Here's an additional question for you all: If steam is that great and verstaile, then what makes the TFH sell and which industries use widely this type of heaters?

As far as I know steam boilers and hot water boilers etc. can be used almost in every industry. Then, why some customers still buy TFH even in non-dessert locations and areas?

Also, check the chart shown in the link below:

http://www.ttboilers...Thermal_Oil.htm


Best,

[djack77494]

Even though steam and hot water are wonderful heat transfer and storage fluids, there is no one answer fits all. In Alaska, steam is very rarely used due to worries about freezing (though it is successfully used in other cold weather regions). They probably had a bad experience once and that lingers in the mind of someone with a great deal of influence. This is often the reason behind some of these decisions. (We should always remain flexible and open to new ideas or revisiting old ideas).

Probably the most common reason for using a HTF, especially at high temperatures, is because you can reach high temperatures without the need for high pressures. With hot water, the maximum temperatures are limited. With steam, higher temperature = higher pressure as fixed by the steam tables. With HTF's, you have so many formulations that you can custom design a fluid that will meet your needs. There are lots of other reasons as well; I'm just trying to offer a few of the more likely candidates.

[Padmakar Katre]

Even though steam and hot water are wonderful heat transfer and storage fluids, there is no one answer fits all. In Alaska, steam is very rarely used due to worries about freezing (though it is successfully used in other cold weather regions). They probably had a bad experience once and that lingers in the mind of someone with a great deal of influence. This is often the reason behind some of these decisions. (We should always remain flexible and open to new ideas or revisiting old ideas).

Probably the most common reason for using a HTF, especially at high temperatures, is because you can reach high temperatures without the need for high pressures. With hot water, the maximum temperatures are limited. With steam, higher temperature = higher pressure as fixed by the steam tables. With HTF's, you have so many formulations that you can custom design a fluid that will meet your needs. There are lots of other reasons as well; I'm just trying to offer a few of the more likely candidates.

Dear DJack,
Great Addition. Thanks.

[kkala]

Probably the most common reason for using a HTF, especially at high temperatures, is because you can reach high temperatures without the need for high pressures. With hot water, the maximum temperatures are limited. With steam, higher temperature = higher pressure as fixed by the steam tables. With HTF's, you have so many formulations that you can custom design a fluid that will meet your needs. There are lots of other reasons as well; I'm just trying to offer a few of the more likely candidates.

Quite agreed. Water treatment requirements go stricter and stricter with increasing pressure. A power plant will decide high pressure steam to produce electricity, but a chemical plant needing high temperature heating can use a salt heater instead.
In alumina plants diasporic bauxite pulp is leached (digested) at temperatures up to 290 oC. Technologies use either salt heaters or high pressure steam. From a comparison in 1990, I understood that salt heaters could have better control, as well as some economic advantage in operating cost. There is always some condensate mass loss in the network and the subsequent condensate treatment, while salt losses (as % of its holdup) were quite low. Nevertheless salt heaters are very limited compared to boilers, due to mentioned advantages of water. Even for above said digestion more technologies used steam than salt heater (1990). Salt heater is "advanced technology" compared to steam generation. I have not heard of any salt heater installed in Greece.

[Duratherm]

We sell heat transfer fluids so of course we might be a little biased but I was just reading this article on Chemical Processing Magazines site that might have a different perspective.

chemical processing article

There are plenty of good points raised here for both the pros and cons of both steam and heat transfer fluids/thermal oils and at the end of the day I think it just comes down to the specific application and resources available.

If you're looking for thermal fluid systems we have a list of manufacturers here

http://www.heat-tran...uthtf/links.php

Edited by Duratherm, 28 February 2011 - 11:55 AM.