Tempco Blog articles

Preventive maintenance for heat exchangers efficiency

Preventive maintenance is a very hot topic nowadays, or even predictive maintenance where Industry 4.0 concepts are adopted with data collection and analytics using AI in IoT industrial production contexts. A proper maintenance enabling the prevention of potential problems on industrial machinery and equipments is indeed essential in order to avoid downtimes in production, with related high economic losses.

In case of plate heat exchangers, preventive maintenance can in addition ensure relevant advantages in terms of energy saving, because it ensures to leverage the thermal transfer at its maximum efficiency, as it was originally designed.

The monitoring of some key parameters allows in fact to evaluate the most suitable moment to proceed with a maintenance intervention:

  • increasing values of flow rate pressure drop, compared to design values
  • diminished performances in terms of output temperature levels, compared to design values

Scambiatori a piastre fouling sporcamento manutenzione preventiva

 

These are two main KPI to check in order to determine if the exchanger need a cleaning and washing service. These two parameters are a key indicator for each kind of heat exchanger: at same capacity, is in fact clear that fouling and scaling on thermal transfer surfaces cause an increase of the pressure drop, being it the pressure difference between inlet and outlet of the fluid. In addition, the thickness of the scaling generates a sort of isolating effect, decreasing the thermal transfer efficiency rate of the exchanger.

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High precision thermoregulation in mono fluid mode

The employ of mono fluid thermoregulation is very much common in pharmaceutical and chemical industries production processes, used for the temperature regulation of reactors. Many and diverse are the applications, as these can involve small reactors used in laboratories or big reactors for the production of APIs, but also mixers employed for the mixing of chemical matters or cosmetics.

The basic concept of all these applications remains anyway the same, being it to maintain these systems at a certain temperature to prepare the product inside them thanks to a series of increasing or descending ramps of temperatures, with controlled cycles of heating and cooling.

Reactors are usually jacketed, and a fluid can flow inside the jackets, hot or cold, in order to heat or cool the product on the inside. A simple primary solution is to let different fluids flow within the jacket, for example steam and cold water, to achieve the temperature regulation. But during the switch between the fluids, the jacket must be completely emptied, avoiding potential contaminations of the fluids, and the new fluid must be pumped to completely flow inside the reactor, involving additional technical times.

The best solution is therefore to employ mono fluid thermoregulation, using a unique fluid that continuously flows inside the jacket that step by step gets thermoregulated at the right temperature required to heat or cool the product, by means of heat exchangers and switching valves. Based on a set-point configured by the production of the customer on a PLC, which is connected with the thermogulating unit, valves on the steam exchanger are opened in order to achieve heating, or otherwise commanding the valves on the cold water to cool the fluid that keeps on circulating.

There are clearly several and diverse systems, for example thermoregulating units with electrical heating section and cooling with water, or multiple stage thermoregulating units, steam heating or cooling with tower water or icy cold water, if very low temperatures must be reached. In fact, these are extremely customized thermoregulating units, even considering the fact they often operate in safe or Atex environments, or they are intended for installation within the United States, requiring UL certification, or in the Russian market, needing to be compliant with EAC regulations.

But after all the working principle remains the same, a unique fluid that keeps on circulating on the reactor side, getting heated or cooled by utility fluids that are fed into the thermoregulation unit. The advantages of mono fluid thermoregulation is therefore to have a constant circulation of the fluid, no contamination of working thermal fluids, and finally the possibility to achieve a wide thermoregulation range. With a very precise regulation of temperature and a fine control of the set-points, with strict tolerances, thanks to the use of PID systems, switching valves and highly accurate regulation systems.

Mono fluid thermoregulation in refining plant

Special project for a mono fluid thermoregulating unit in a precious metals refining plant. The unit is aimed at the thermoregulation of reactors. Reactors’ level of temperature is maintained using an array of brazed plate exchangers, using steam as working fluid on the heating circuit and icy cold water on the cooling section. The kind of application involves a very harsh and aggressive working environment, therefore the selection of the kind of materials to be employed has been made based on the long experience and in depth know-how that Tempco has gained on the field, achieving the required goal thanks to the close collaboration between the plant management unit of the customer and the engineering office of Tempco.

Tempco termoregolazione monofluido reattori

In this particular application, the working range has been pushed up, being it a thermoregulating unit that employs pressurized water at a working temperature of 140/150° C, which has to be maintained even for very long process cycle times, leading to very demanding operations.

The brazed plate exchangers installed in the thermoregulating unit are the result of a special engineering, regarding both the layout of the circuit and the design, due to the fact that they have to endure very wide temperature variations, often exceeding 130° C.

Tempco termoregolazione monofluido reattori render

Tempco termoregolazione monofluido reattori scambiatori

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Fluids and carbon steel in plate heat exchangers

How connections on plate heat exchangers are made to avoid contact between the fluid and carbon steel? This is a question that I’m often asked for.

If the fluid employed within the exchanger presents no particular problems in getting in contact with carbon steel, the fluid entering the flange of the exchanger gets then in direct contact with the material. Thereafter, it enters the exchanger and here it gets in contact with the stainless steel of the plates. But very often, it is necessary to avoid the contact of the fluids with components and materials that are prone to oxidation and corrosion. In this case, it is mandatory to avoid any possible contact of the fluid with carbon steel

Plate heat exchangers can have two main connection options, with flanged or threaded connections. Flanged connections make the trick quite easy, in fact it’s sufficient to coat the body in the nozzles area using elastomers, such as nitrile, ethylene-propylene or viton, or using stainless steel AISI 304 or AISI 316. The inner part of the body in the nozzle area is protected as well by this lining. The gasket of the first plate gets then in contact with the circular ring of this lining, so that the fluid flowing through the body enters between the first two plates, never getting in contact with carbon steel. The final plate is a blind plate, so it never gets in contact with carbon steel either, remaining always in contact only with the plates in stainless steel.

Speaking of it, fluids never flow between the first plate and the body, they always enter directly between the first two plates.

On plate heat exchangers with threaded connections, the nozzles – made in stainless steel or using plastic materials in case of aggressive fluids such as sea water or acids – have a sort of counterpart which gets in contact with the gasket, and is held back by the body. So that here as well the fluid entering the exchanger gets only in contact with stainless steel and the materials of gaskets. Never getting in contact with carbon steel, paint or other materials that are prone to corrosion.

Finally, the problem doesn’t even exist in plate heat exchangers for food and beverage applications, where hygienic requirements force to employ full stainless steel executions.

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Immersion cooling and towers in die casting foundry

Back in 2011, Tempco installed a cooling plant for an important Italian foundry. The cooling plant provides in fact the cooling of several equipments, including induction furnaces, die casting machines for the foundry of metallic parts with steel dies, moulds cooling tanks and cooling tanks for the manufactured parts.

Overall, the cooling plants is composed by:

Tempco raffreddamento fonderia torre di raffreddamento

 

After more than 10 years of operations, the customer needs to increase the production capacity of the plant. The intervention involved to double the cooling tower and the related water distribution system, due to the fact that the foundry will install new additional induction furnaces and also because the cooling system will have to serve also a new part of the plant aiming for the cooling of die casting machines.

Tempco raffreddamento fonderia conchigliatrici parti metalliche

Tempco raffreddamento fonderia scambiatori TCOIL a immersione

Tempco raffreddamento fonderia scambiatori saldobrasati

 

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How to calculate a thermal buffer tank in process cooling

How a thermal buffer tank gets calculated, and what it is aimed for? Buffer tanks, or inertial storage tanks, are employed in cooling systems with thermoregulating units served by chillers. Very often, indeed, our thermoregulating units, or thermostatation units, are served by chillers to serve utilities such as pharmaceutical reactors or industrial processes in general. These cases involve high temperature gaps, requiring within the same process cooling tasks, heating and maintaining a certain temperature.

Let’s do an example of a pharmaceutical reactor where a product has to be heated at a high temperature, for example 90° C, in order to achieve a certain chemical reaction. Once it’s done, the product has to be kept at a certain high temperature for a defined time lapse, and then cooled. We have therefore a high volume amount of product at high temperature and a jacket of the reactor with a circulating fluid at a high temperature as well, and it all has to be cooled. What happens is that the thermoregulating unit closes the heating section and opens the cooling section, by means of a valve, a 2-way, 3-way, switching or on/off valve, on the exchanger.

The refrigerating group is sized in order to achieve the cooling of that exact mass volume of product within a defined time lapse. But as soon as the cooling process starts, we suddenly have an enormous amount of fluid at high temperature entering the exchanger, where cold water flows on the secondary circuit. The exchanger will therefore transfer a huge amount of thermal energy, due to the fact we have a very high logarithmic mean temperature difference, that increases the efficiency of the exchanger. The overall amount of thermal energy gets then discharged upon the cooling water, and in case there is no availability of a storage tank with an important volume the risk is to put the chiller under a high stress.

This is because, if we have a limited volume available, all of this energy gets dumped inside the cold tank, and the water, instead of returning the chiller at a temperature of 15° C, for example, to be cooled at 10° C, comes in at a temperature of 40-45° C, or also 50° C for a transient. Which is enough to bring the evaporation pressures of the chiller out of its working range, thus blocking the refrigerating group and stopping the cooling process required by the production.

It is therefore very important to properly calculate the volume of this storage tank, or buffer, in order to have an inertial tank able to diminish these peaks. Allowing to provide water to the chiller at a temperature that doesn’t create a stressing task. The calculation is made by considering the mass volume of the product, and then the amount of energy, maintaining a margin on the volume of this tank in order to ensure that, during these peaks, the temperatures remain within the operating range of the chiller, 20-25° C, 30° C at maximum.

At this purpose, it’s important that the customer helps providing all the basic informations about his plant, such as the volume of circulating water, the length of pipings, the volume of the reactors, in this case, and the speed required to achieve the cooling process. This is all necessary to correctly size the dimensions of the chiller. Finally, it is also helpful to have a 3-way switching valve on the cooling section of the thermoregulating unit, allowing to set a temperature ramp that respects the temperature and the time lapse of the customer, and allows the chiller to work properly without going under excessive stress.

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Multi pass plate heat exchanger for hydraulic power unit

Pictured here below is an important plate heat exchanger, that Tempco has supplied to serve a hydraulic power unit. This is a quite remarkable machinery, as easily arguable from its main characteristics:

  • Oil flow rate of approx. 2.500 lt/min ISOVG46
  • Cooling water at medium-high temperature with limited flow rate
  • Installed power capacity of approx 1.700 KW

The limited flow rate of the cooling water has in particular involved a demanding thermal scheme. The application required indeed the engineering and realization by Tempco of a special multi pass plate heat exchanger with DN200 connections. The exchanger is equipped with plates with a thickness of 0,6 mm and NBR HT gaskets.

Finally, the equipment is in PN16 execution.

Tempco scambiatore multi pass Centrale idraulica

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Wind chill and evaporative towers

When I try to explain how evaporative towers work, I often find myself speaking about that particular effect called Wind chill, also useful to show the advantages of cooling towers compared to indirect heat exchangers.

The wind chill, or cooling effect caused by the wind, refers to that sensation of chilling coming out from a swim in the sea in the presence of wind. This sudden and intense sensation of cold is caused by the evaporation of water over our body, and this is due to the effect of evaporation of water on our skin that absorbs calories, energy.

This is exactly the same effect that happens in adiabatic coolers and evaporative towers, that allows to cool water at a temperature level lower than the temperature of ambient air. In fact, speaking about evaporative towers with customers, we always ask them the value of design wet bulb temperature, which is essential aimed to design and calculate the cooling tower.

Watching US’ standard ASHRAE tables, or also other climatic tables, there are always average dry bulb temperatures indicated referred to different geographical areas, both during the winter and summer season. These tables contain as well a column with the respective average values of wet bulb temperature.

Making it simple, wet bulb temperature is the temperature that is obtained wrapping the sensor, or bulb, of a common outdoor thermometer with a slightly humid rag. Suddenly it will be possible to see the temperature’s level going down, and this is the wet bulb temperature, that is the temperature of the bulb humidified, which is lower than ambient external air temperature. This is as well the reference temperature employed for the design of cooling towers, because that’s the lowest temperature that can be achieved, obtaining water coming out of the tower at a lower temperature. It happens taking advantage of the latent heat of vaporization, which is the energy that gets dissipated by water to evaporate, generating a decrease of the temperature of the water that gets cooled.

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Cooling for power inverters in Russia with special shell and tube exchangers

We have recently supplied a series of shell and plate heat exchangers aimed for the cooling of power inverters, according to the special requirements received by the engineering company that commissioned the plant.

The final location of the application is in Russia, where EAC certification is required for industrial equipment installation, which in Tempco is available as a standard option on our full offering of heat exchangers.

Scambiatori fascio tubiero raffreddamento inverter EAC

The shell and plate exchangers employed present in addition a particular construction, because the tube array inside the exchanger is made using a series of tubes with a spiral shape, aimed to achieve a double target:

  • increase of thermal transfer rates thanks to the turbulent flow of fluids
  • thermal expansion compensation ensured by the particular shape of the tubes

Scambiatori fascio tubiero raffreddamento inverter Russia

Scambiatori fascio tubiero EAC raffreddamento inverter

The exchangers are completely constructed using stainless steel.

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Double wall exchangers and oil hydraulics

Double wall heat exchangers are a particular kind of exchangers that is also employed in oil hydraulics applications. The main characteristic of these exchangers is to have a double plate, or double wall, to avoid the possibility of mixing between primary and secondary fluid in case of breaking, corrosion or perforation of the plates.

This kind of exchangers is employed in hydraulics plants especially in case of extremely sensitive applications. An example is the cooling of the hydraulic oil of a gearbox in a turbine for power generation, where the mechanical component is a core part of the application. In this case, having the presence of water within the oil leads to irreparable damages.

The most common solution employs tube-in-tube shell and plate exchangers, double tube then, or double wall. These exchangers have special heads that, in case of leakage of fluids, allow the leakage to flow within a special chamber between the two heads. Allowing the detection of the leakage and a prompt repair intervention.

In case of double wall plate heat exchangers, the presence of a double gasket in the nozzle area avoid the possibility of fluid’s mixing. In case of breaking of a gasket, indeed, along the external perimeter of the exchanger or in the nozzle section, the leakage flows towards the outside of the exchanger. In case of cracking of a plate, there is an air chamber passing between the two plates, with therefore a visible leakage of fluids toward the outside, making it easy to repair it.

Advantages and disadvantages of the double wall solution. The advantages are all related to the security, making double wall exchangers a mandatory choice when is strictly necessary to avoid any possible mixing between the primary and secondary fluid, in this case hydraulic oil and water. The disadvantages are many, on the other side, first of all the higher costs due to the fact that the number of plates gets duplicated. Thus increasing the amount and costs of construction materials. In addition, having a higher thickness and an internal chamber air between the two plates, the thermal transfer coefficient rates are lowered. And so, not only a higher amount of construction materials is needed, but also the thermal transfer surface must be increased, in order to achieve the same thermal duty. Anyway, it remains a necessary solution to prevent any possible problem of fluid’s mixing, protecting the oil hydraulic plant from serious issues.

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