Thermal energy and industrial processes, a guide

Tempco operates since many years in the field of thermal energy management in industrial processes, with a solid know-how and expertise and several applications in all kind of industrial sectors. Every day we are committed in solving heating, cooling, dissipating, thermoregulating and heat recovery matters.

We wanted to collect and share our know-how in a Manual, Energia termica and industrial processes (Italian language only), aiming to offer a first guide to engineers and designers helping them in the choice of the best suitable thermal machine for their specific application.

Energia termica e processi industriali Tempco

The Manual offers a wide description of all the main thermal machines, heat exchangers, chillers, cooling towers, thermoregulating units, dissipators and free coolers. Each solution is described in its characteristics and related advantages, completed with a series of case histories developed by Tempco along the way.

 

manuale Tempco energia termica indiceA section is in particular dedicated to the evaluation of thermal capacity of a machine, essential step in order to choose the machine itself and the kind and dimensions of heating/cooling components.

Flexibility and customization capacity complete the ability to suit the best thermal energy management solution in order to fit any customer’s production process need and requirements.

Pipe expansion in exchangers connection pipes

Following last week’s post about the function and importance of expansion tanks in thermal oil equipments, when working with high temperature fluids is also important to take account of thermal expansion coefficients of pipes.

allungamento tubazioni espansione termica

Here is a technical table reporting the values of thermal expansion of pipes for different metals, to be used during the design and engineering of heat exchangers connections.

Pipe thermal expansion

Employing thermal expansion joints can help compensate and absorb the dimensional variations on connection pipings, that can be important due to the high temperatures achieved by the diathermic oil in the plant.

Function and capacity of expansion vessels

Heat transfer fluids employed in thermal machines increase their volume while being heated. This effects in particular heat transfer oil that have a high expansion coefficient, thus requiring to provide the plant with an expansion tank.

vaso espansione olio diatermico

 

The presence of an expansion tank allows not to exceed design pressure values on the system. In order to maintain the mechanical and chemical properties of the diathermic oil, some measures can be adopted to avoid the oxidation of the fluid in contact with air in the tank. It can be achieved with a proper piping connection and leaving a minimum surface in contact with air, by using a vent. The air remaining inside the vessel generates a layer that gives up a limited oxygen quantity to the oil, becoming inactive.

This is a simple and cost-effective solution compared to the cooling of the expansion tank, and by far less complicated than pressurizing the vessel with nitrogen.

 

 

 

Expansion tank capacity evaluation
The capacity of expansion tank must be calculated based on two main factors:
– The high expansion coefficient of the thermal fluid
– The overall capacity of the system

Considering a temperature of 300° C, the capacity of the expansion tank must be approximately 30-50% of the overall volume of the cold transfer fluid employed to be heated. This evaluation allows a quiet fair margin of safety.

The diameters used on the relief piping are also important, based on the plant potential, in order to avoid accidental over-pressure that can occur hampering the natural expansion flow of the oil.

Here is a simple technical table with some recommendations:

expansion tank heat transfer oil

Another important factor to be accounted is the pipe length changes due to thermal variations within the system, which will be properly treated in a future article.

Power transformers and cooling fluids

Transformers work as oil-immersed electrical equipments.
The transformer oil is a special kind of oil aimed to both cool and insulate the windings of the power transformer, and must be maintained at a proper temperature using oil/air heat exchangers.

trasformatori di potenza olio raffreddamento

The cooling oil employed in transformers is a highly refined mineral oil with high dielectric strength, thermal conductivity and chemical stability, and its formulation contains pollutants so that it must be carefully contained and monitored.
Exposed to high electrical and mechanical stresses, and also subject to chemical contamination due to interaction with windings at high temperatures, the transformer oil can loose its properties and there are many companies specialized in the analysis and testing ensuring the right management and monitoring the life expectancy of this kind of special cooling fluids.

scambiatori di calore recupero energetico rigenerazione olio trasformatoriIn collaboration and supporting the main Italian company in this sector, Tempco developed plate heat exchangers dedicated to the energy recovery combined to oil regeneration for electrical equipments.
The exchangers hava some special features:

  • Special multi-pass execution ensuring maximum heat recovery efficiency
  • Gaskets in special material resistant to electrical machine oils
  • Plates with chevron angle design suitable for high viscosity oils, optimized in order to avoid pressure drops and maximizing thermal efficiency

Thermoregulation in critical pharma application

We recently supplied a number of thermoregulating units to a leading pharmaceutical company, aimed to regulate temperature on a series of reactors employed in a strategic production process.
The production presents some very critical temperature regulation requirements.

Termoregolazione farmaceutico

The criticality is not depending on the temperature levels, as the thermoregulation unit works on a set-point between +15 and +75° C.
Working fluids are warm water coming from a boiler and from a chiller, already in use in the production facility for other technical purposes.
The specific pharma application is critical because the thermoregulation must be constant and ensured upon any circumstance. This mandatory requirement led to a special design with a double automatic stand-by pump, in order to ensure in any case the constant temperature regulation.

pharma temperature regulation Tempco

 

termoregolazione settore pharma Tempco

The system also features two modulating control valves managed by a thermoregulator, respectively employed on the cooling and heating circuit, maintaining a constant temperature in a range of +/-1°C referred to the current set-point.
After the setting phase, the production in series will start, also including an additional variant with electrical heating.

How to… correct commissioning of Thermoregulating units

The commissioning phase of a TREG Thermoregulating units employing diathermic oil as heat transfer fluid is the most delicate and critical step in the whole plant’s lifespan, as the most serious issues can happen here. That’s why is fundamental to carefully follow the right steps for the correct commissioning of a thermoregulating unit, avoiding problems such as cavitation and leaks.

commissioning centraline termoregolazione TREG olio diatermico

First step: checking of all the electrical and hydraulics connections, and the right filling of the plant. With the machine being cold, let’s turn on the oil recirculating pump, in order to verify the correct inlet pressure, that must be constant. Working pressure and power consumption, with cold machine, will naturally be higher compared to values at standard use.

Second step: very slowly warm up the oil, approx. at +30°C every hour. This is a crucial process in order to completely eliminate the presence of air and moisture in the hydraulic circuit, through the expansion tank. The process will avoid the creation of vapor pads, foaming and possible oil overflow due to excess of filling. These events happen violently and out of control, so that’s why is very important to slowly increase the oil temperature.

 

unità termoregolazione TREG avviamento

 

Third step: once reached the temperature of approx. 100-110° C, further slow down the temperature increase, allowing the complete draining of water vapor. Relief valves must in some cases be opened, especially where vapor bags can develop, in particular if cavitation or sudden inlet pressure variations occur.

 

commissioning circuito termoregolazione olio diatermicoFourth step: regulate the set-point of the thermoregulating unit in order to warm up the oil at approx. 200° C, maintaining oil circulation at this temperature for about 1-2 hours. It allows to:

  • Completely remove moisture in the circuit
  • Completely expel air bubbles from the hydraulic circuit
  • Checking possible leaks on the oil circuit

Finally, once the circuit has been turned off and the system has returned to the initial temperature, verify that all the seals and fastenings are correctly performing, fixing possible leaks.
The thermoregulating unit is finally ready to operate.

 

 

 

TREG units and heat transfer fluids, advantages and critical points

Among the many kind of heat transfer fluids employed in heating, cooling and thermoregulation applications, heat transfer fluids, such as diathermic oil, offer a wide range of advantages. Diathermic oil is widely employed today in industrial applications of Tempco’s TREG thermoregulating units, in substitution of water and vapor to better meet the needs of more advanced technologies and production methods, requiring a wider range of working temperatures.

olio diatermico termoregolazione

Heat transfer fluids are mineral or synthetic oils with special thermo-physical properties, compared to water and vapor, such as a high boiling point, approx 400-500° C, low vapor pressure and low pour point, reasons why they are widely used as a heat carrier in heat transfer systems.

The working life span of a diathermic oil and its performances are strictly depending on a number of factors, such as a proper engineering and sizing of the termoregulating unit, taking account of the peculiar chemical-physical properties of the specific heat transfer fluid involved. Other crucial elements are the selection of the correct materials, suitable for use with the heat transfer fluid, a correct filling and warm-up of the plant in the starting phase, and finally a careful maintenance.

termoregolazione fluidi termovettori

And here is a list of the main advantages achievable with diathermic oil in TREG thermoregulating units as a heat carrier:

High temperatures resistance
– Working at atmospheric pressure
– No PED compliance required (no pressurization)
– No chemicals and conditioning required
Low freezing point and no risk of piping breaking in case of extreme low temperatures
– System startup at low temperature
– No scaling nor corrosion, if properly used
– Common construction materials (carbon steel)

On the opposite, diathermic Oil in thermoregulation and heat transfer systems also entail some disadvantages to be accounted, such as:

– Low specific heat compared to water
– Flammability
– Need of a recirculating pump
– Higher costs, especially in case of high capacity volume plants
– Craking and contamination risks related to bad operations

 

Legionella, risk avoiding and prevention

Due to the sadly recurring news about further cases of Legionella infections, we return on the topic of how a proper maintenance of cooling plants is crucial aimed to the safeguard of public health.
The BN 111U product employed by Tempco for evaporative towers purification is a specific active bactericidal, antimicrobial and algae treatment for humidification and rain test chambers, cooling circuits and paper mill processes.

 

Legionella trattamento antibattericida Tempco BN111U
The product TC BN 111U by Tempco is particularly effective for the treatment of Legionella Pneumophila bacteria, both for use as initial antimicrobial Legionella treatment and in a successive prevention program.

The product can be employed in a starting shock dosage aimed to completely eliminate all the existing bacteria, to be repeated every 2-3 days until complete control of the bacterial proliferation. Further following shock dosages can be used as a prevention treatment. Also a continuous dosage treatment in the system can be adopted for legionella prevention.

 

battericida antilegionella BN111U Tempco

 

The product can be added manually or automatically, employing a timer-controlled dosing pump.
The technical sheet of the TC BN 111U product reports in details the correct employ mode and dosage informations both for eliminating existing Legionella bacteria and for an effective successive Legionella prevention.

Heat to electricity, the disruptive technology of Rectennas

Producing electricity harvesting heat with a device without moving parts could soon be a reality, thanks to several studies on development in laboratories all around the world on optical Rectennas. The Rectennas are a disruptive technology consisting in micro-antennas able to capture the electromagnetic waves at optical frequencies of infrared, produced by any object emitting heat, directly transforming thermal energy into electricity for efficient heat recovery.

Paul Davids Sandia National Laboratories Rectennas

A prototype of Rectenna has been recently announced by the physicist Paul Davids of Sandia National Laboratories in a publication featured on the Physical Review Applied. The micro-antenna developed, the size of a small finger nail, is made of aluminium in the upper side and by silicon doped with other several elements in the lower side, reflecting the infrared radiation. The addition on the lower face of a layer of 20 molecules of silicon dioxide works as a rectifier diode, capturing the alternating flow of electrons to create a current flow. The rectenna has been optimized and constructed employing materials of high availability and common use as much as possible, with methods allowing a production by actual semiconductors industries.

 

Rectenna thermal energy harvestingOptical rectennas thus represent a highly interesting alternative to thermoelectric generators, electrons generators from heat employed to power spacecrafts, requiring high temperature gaps in order to function, with high construction costs and offering low efficiency. Rectennas production could be cost-effective and practical, also at an industrial level and in bigger scale compared to the Davids’ prototype. This kind of device is also very reliable, and unlike electromagnetic generators doesn’t need to be in contact with the thermal energy source, thus less exposed to thermal stresses.

 

 

 

 

By capturing the infrared radiation, coming in continuous from the Sun and also dissipated by the Earth itself at night, the rectennas could operate as a sort of innovative photovoltaic technology producing electricity 24/7. At the moment Davids is looking forward to applications on harvesting heat from thermal plants, or to power devices such as spacecrafts that employ radioisotopes. Many years of further development are necessary in order to apply rectennas on harvesting sunlight and infrared radiation during the night time.

torri evaporative energia termica

Interesting advancements are anyway coming in several other laboratories around the world, such as the prototype of an optical rectenna aimed for sunlight harvesting developed by the Connecticut University, of the rectenna developed by Baratunde Cola in 2015 at the Georgia Tech Institute. The Cola’s rectenna is a carbon nanotubes antenna coupled with a diode composed by a layer of calcium, recently further enhanced settling a bilayer material composed of alumina and hafnium dioxide, increasing by 1.000 times the capacity, switching the current production from microvolts to millivolts range. According to Cola, optical rectennas could then be used to operate low-power sensors and powering IoT devices.

Legionella and cooling towers maintenance

Strictly related to cooling towers maintenance, as well as of HVAC and cooling equipments, the problem of legionella infections returned as an emergency last July in the north of Milan, in Bresso, with 11 persons hospitalized at the near Niguarda hospital. The Italian ISS, the Superior Institute for Healthcare, reports an increase by 17% of legionellosis in 2017 in Italy, compared to 1.700 cases occurred in 2016.

torri evaporative prevenzione legionella

Legionella is a group of bacteria commonly present in aquatic environments, that proliferates in presence of air and water at temperatures in a range between 25 and 50° C. The Legionella disease is transmitted by aerosol inhalation of a contaminated source, small droplets that are commonly found in HVAC and cooling machinery or with cooling and evaporative towers. A proper and correct maintenance of cooling towers is thus mandatory, in order to reduce the risk of infections.

legionella prevenzione

 

The measures are diverse, ranging from technical solutions such as the adoption of efficient drop separators, a construction of the plant that allows high accessibility for cleaning and service, avoiding stagnation points with proper drainage, and finally a water purification of the plant. Towers’ maintenance thus ensure not only maximum efficiency operating conditions of the cooling plant, but also a healthy environment where the evaporative tower is installed.

cooling towers legionella preventionThe IIS reports other cases of Legionella disease in the past: in 2016 in Parma a total of 42 cases of infections were related to a cooling tower of a local posts office. Many cases happened in Cesano Maderno, near Milan, from 2005 to 2008. The cause was not clearly identified, but infections stopped with the closing of many industries during 2008. At last, a Legionella epidemic happened in Rome in 2013, with 15 cases, due to a cooling tower of an important local commercial center.