Comparison between thermal fluid and steam

In previous posts we informed on the thermal fluid transmitters that can be used in an industrial installation. In this blog we want to make a comparison between the use of the thermal fluid versus the steam, both perhaps the most extended systems world-wide.

The requirements for the steam facilities are more restrictive than those of thermal fluid:

• Steam boilers of a certain size and water volume have to be installed in a separate boiler room. In many countries the boiler room cannot be located within the main building or production site, but has to be separated at a certain minimum distance. Moreover, protection walls of such boiler room have to be of a minimum thickness, depending on the category of the boiler.
• Water treatment is an absolute requirement for every type of steam boiler, whether of the coil type, water tube or fire tubes. Water treatment consists of a water softening plant (which should be a twin system in most of the cases) in combination with a chemical treatment of pH control and oxygen scavenger. A water softener “Twin” system consists of two cylinders to hold the resin in order to allow a regeneration of one column whilst the other resin column remains in service. A twin softener is an absolute must in production plants with a continuous operating cycle of 24/24 h.
• Oxygen removal and pH control can be done by means of a chemical dosing system (dosing pump with dosing tank). With some type of boilers, especially of the coil type, special care has to be given during “stand-still” periods. If no measures have been taken to keep the coil either completely dry or completely filled by means of a time controlled “post-run” system, the risk of oxygen corrosion during standstill period is very high. (Note: Post-run means that the water pump has to remain in operation to keep the coil filled with water whilst the system cools down, in order to prevent air pockets to be formed in the upper part of the heating coil which would introduce oxygen in the heating coil and cause a typical form of “pit corrosion”).
•  With too much concentration of TDS (Total Dissolved Solids), a carry over of chemicals will take place. Too high concentration of dissolved solids (example over 3.000 mg/l) can be caused either when blow down periods are not being strictly adhered to or during “peak-loads” which demand momentarily more steam than the average nominal capacity of the boiler size. This carry-over will result into wet steam and the chemicals which will remain in “wet steam” can block steam traps, steam regulating valves etc. Hence, high maintenance costs and waste of energy in case steam traps do not function properly and do not shut off properly.
• Some more details are referred to in the section “Corrosion” hereafter. Especially in fire tube boilers, because of the larger water content, explosion risk remains despite added automation on modern boilers.

Efficiency

The thermal fluid does not require any special treatment once the installation has been filled up. Its life oscillates between 10 and 12 years. This means that the cost of this element is really insignificant.

The thermal fluid, which comes out of equipment after having heated it, will enter into the generator with only 1 or 2 ºC less temperature. This shows that the loss of heat during its way in the line is situated at the minimum.

There has to be taken into account, that the outcoming steam of a purge has an average temperature of 120 ºC, whereas when it reaches the tank of condensed it usually does not exceed 90 ºC, and in many occasions it does not even reach this low temperature. On the other hand it should also be taken into account, that there always remain a flow of steam in the purges which gets lost through evaporation and these calories are never more recovered.

Thermal fluid systems suffer none of the above-described losses.

Legal requirements

These are generators working WITHOUT HIGH PRESSURE. This fact exonerates them of the walls, distances to neighborhood, and all the other norms which have to be taken inTO account and accomplished for the steam type boilers. Thermal fluid boilers may be installed in any place, even just besides the manufacturing machines.

Corrosion

Neither the generator nor the pipeline suffer from wearing away, as the function is done with lubrication liquid, NOT CORROSIVE like water.

Maintenance

Any kind of dragging, such as for water, of salts, of oxides, or of any other indissoluble solids is not necessary. This means that nothing can affect the goodness of heat transmission through thermal oil. This type of installations are practically free of maintenance.

Fuel saving

When heating is done through thermal fluid, we are able to obtain a level of temperature regulation till ± 2 ºC in the machines. When using steam heating this is completely unthinkable, as the differences in a normal installation are situated around ± 10 ºC.

This is of course also a very important factor in saving fuel, as it allows organizing a very regular temperature average, without any fear that the quality of the product may get spoiled due to the ups and downs which could occur when treated with steam.

The sum of the related factors results on a fuel saving around a minimum 12 to 18% according to concrete data taken in facilities which are working for a long time to total satisfaction of our clients.

Technology

Another advantage when using thermal fluid, is that all problems concerning passing preferences, as usually they appear in steam installations, are completely cancelled: When working with steam all the machines, which are located nearer to the boilers, they will receive the full amount of flow which they need. Those machines which are at a greater distance very often have a lack of flow.

With the thermal fluid and through our system of ballast check valves we assure to each individual machine the whole quantity of necessary hot oil, ensuring a temperature stability.

Safety

No risk of explosion, because there is no high pressure inside and neither hot oil storage.

Cavitations do not appear in the recirculating pump of thermal oil.

In steam installations they may arise when the feeding water which is recovered from the condensed surpasses a temperature of 90 ºC, at that stage either it is cooled down with water entering in the line or part of the condensed are thrown away, but this last supposition is really absurd in view of the cost of the fuel.

With the details we have mentioned above, we intend to offer you a global view on the subject of the thermal fluid installations. However in order to get a more precise knowledge it is necessary to enter deeper in this kind of equipment, for this purpose we remain at your entire disposition. Read More!

Heat transmission fluids (2)

SMOKE or GASES. This source of heat is used generally when a surplus of energy in the form of smoke or hot gases exists.

In those cases, it is profitable to invest in a recovery unit or economizer that helps to reuse the heat that those smokes contain. Its design will be adjusted to the final application to which the residual heat will be destined. To do this, the recovery unit has coils, chambers, etc. through which water, air or any other fluid that it is interesting to warm up for other subsidiary process in the plant, will be forced to circulate.

Applications: Fuel saving by an industrial burner as a result of the preheating of the air used by it, for example, or, as a central heating or air conditioning of a plant, etc.

Water heating, steam production, etc.

The recovery systems are usually provided with a by-pass or diverter, to interrupt or to turn aside the smoke flow of its passage by the economizer or heat recovery unit.



THERMAL OIL. There are two types, synthetic and mineral, being different marks and models in the market, to work to different temperature ranks. We wrote about in a old post about the thermal fluid transmitters of heat.

The main characteristic of the oil is that it does not change of state when working over 100ºC under absolute pressure, reason why the circuit pressure that it generates it is not as high as the generated by other fluids.

We advise about the use of the thermal oil in processes in which it is needed indirect heat and high working temperatures (from 150 to 300 ºC).

Please remember that at the end of the useful life of the thermal oil, the user must recycle it, but about that we will speak in the next blogs. Read More!

Heat transmission fluids

Following with the thematic developed in our last blogs of year 2009 and to start correctly the present new year, we will speak now about the heat transmission fluids, being the most common:

• Water
• Steam
• Smoke or stack gases
• Glycerin
• Thermal oil
  

WATER and STEAM. The water used in hot water boilers and steam ones (to produce this one) normally needs a previous treatment of decalcification, etc. to preserve the life of the boiler in which they are used, besides, sometimes, continuous purges of muds and foam that the process generates, which derives in energy losses. On the other hand, it usually is at the disposal of the users with facility and in abundance.

Basic characteristics: The water changes of state under atmospheric pressure at 100ºC, reason why if you wish to work with it over that temperature, you will have to increase the pressure, obtaining a product called High Pressure Hot Water.

Something similar it happens to the steam, with a result of the pressure-temperature saturation curve of steam (as example: 150ºC 5 bar a), obtaining in this case High Pressure Steam.

The design of the boilers can be PIROTUBULAR or ACQUATUBULAR, based on what is circulating through the tubes: if there are smokes or water.

In our next blog we will speak about the rest of heat transfer fluids. Read More!

The thermal fluid transmitters of heat

PIROBLOC as specialist in the design and manufacture of thermal fluid heaters and other apparatuses that use that type of heat transmitting fluids, is today interesting to approach them to you and giving you more data on such.

Types:

The synthetic fluids fulfill the majority specific functions. Some of them have problems due to the toxicity, to the high point of freezing or the high viscosity at low temperature.
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The mineral oils fulfill with the next described requirements, a rank of application of temperatures from -10º C to 300º C and an index of viscosity in the rank 0-100 ST.

The basic requirements of any fluid are the following ones:

- They must be thermally stable to the temperature of service.
- It has to have high thermal exchange coefficients.
- The pressure of vapour at the operating temperature must be low in order that the system can work at atmospheric temperature.
- It must have a low viscosity to favour a turbulent work conditions, and at the same time, the viscosity at low temperature must be sufficiently low to favouring the cold starting.
- It does not have to be corrosive nor toxic.
- It must be safe and easy to use.

In reference to the viscosity, it is considered from two points of view: separately and its variation in reference to the temperature.
The oils have advantages in comparison with other fluid, thanks to their better relation viscosity/temperature, that it is expressed in terms of the Index of Viscosity. It is calculated by an empirical formula from viscosities at 40º and at 100º C. A high value means a small change of viscosity in relation to the temperature.

The point of freezing of a fluid measures the temperature to which the oil stops flowing by simple gravity, important factor in relation at the moment of the starting and its properties to low temperatures. In order to reduce this point, most of fluids incorporate additives.

The density is the mass by volume unit. The density is marked in kg/l or g/ml in relation to 15º C. Most of oils have values around 0.85 - 0,9.

The specific heat measures the amount of heat absorbed by unit of weight when its temperature increases one degree Celsius. The oils have values between 0.45 and 0.70 in the rank of temperature of habitual work.

The flash point is the temperature to which, with certain test conditions, a flame applied to the surface of the oil causes the ignition of the vapour but not a continued combustion. It is very important not to confuse this temperature with the temperature of combustion or self-ignition.

Once approximated a flame or spark, the combustion point is the temperature to which, in the presence of comburent air (oxygen), the flame maintains at least 5 seconds ignited. The normal values are located around 210º C.

The self-ignition point is the minimum temperature to which the thermal fluid ignites by itself, without presence of flame or spark that initiates the combustion. Logically, the presence of comburent air is necessary.

Consequently, the temperature to be considered in reference to a possible escape of thermal fluid, it is the temperature of self-ignition.
It’s necessary to have a escape, because without it, there is no oxygen in the circuit and therefore, although we reach temperatures of point of self-ignition in the close circuit, it would not be possible a combustion.

By all it, the probability of a fire in an installation of thermal fluid PIROBLOC, is practically null. The kindness of this affirmation, it comes authenticated by the effective legislation in Spain, which considers the thermal fluids like NO INFLAMMABLE LIQUIDS (B.O.E. nº 120, 20/5/82).

In reference to our thermal fluid circuits, being closed and not existing oxygen presence in them, a combustion or fire is impossible, unless there is a escape.

In the following picture we can observe the characteristic temperatures of the main thermal fluids of the market. We can observe that the maximum temperature of service (indicated by the manufacturer) and the temperatures of flash point and self-ignition do not keep a direct relation:

Please, click in the image to Zoom In.

PIROBLOC supplies the PIROBLOC-A, a thermal fluid with the following typical characteristic:
- Density at 15 ºC: 0,880 kg/l
- Viscosity at 40 ºC: 20 cSt
- Viscosity at 100 ºC: 4,5 cSt
- Viscosity index: 80/90
- Flash Point P.M.: 180 ºC
- Freezing Point: -45 ºC
- Specific Heat 50 ºC: 0,48

In our next blog, we will continue speaking about this subject with special attention to the white fluids (the unknowns by the users).

Read More!