Inflate your air mattresses and have a great August!
In Tempco we wish you this way great Summer!
VIDEO: Inflating TCOIL dimple jacket exchangers
Leave a comment
Self draining Dry cooling, cooling efficiency in every season
We’re facing today the topic of dry cooling, and in particular of self draining dry cooling. First of all, a dry cooler is an air/water exchanger that employs ambient air as cooling media to cool down the temperature of water. Compared to an evaporative cooling tower, a dry cooler offers simple installation, easy management and employs water in closed circuit, never in direct contact with external ambient air. The fluid to be cooled is indeed circulating in pipes, while the exchanger has a fin pack, often with copper pipes and aluminium fins but it’s also possibile to have stainless steel pipes and aluminium fins or both pipes and fins in carbon steel, depending on the kind of application and type of fluid to be cooled (water, water glicol, hydraulic oil, diathermic oil for example).
A dry cooler is in addition a quite economic solution, due to the fact that the only energy consumption is related to the fans ensuring the air flow.
A dry cooling solution has some limits, strictly related to the external ambient air employed to cool down the fluid. During the summer, the outlet temperature of the water can be indeed at maximum 5-10° C higher than the temperature of ambient air.
On the other hand, during the winter, when air temperature goes below 0° C, the risk is that the water inside the pipes can freeze, with severe damages to the plant with breakage of pipes. In this case there are two solutions: if the requirement of the process allows it, is it possibile to employ water glicol, preventing the freezing, otherwise the solution is represented by self draining dry coolers. In this kind of dry cooler the water inside the pipes is automatically and completely drained out of the exchanger, thanks to a sloped exchange pack and to a special pipe battery with valves for the complete discharge of the water.
At last, dry coolers have significantly increased their energy efficiency thanks to developments in the technology of fans, using EC motor fans that during the different seasons provide the proper adjustment of the functioning speed to the weather conditions and to the effective needs of the plant, reducing energy consumption at the minimum required.
Dematerialization and green recovery in the farm
Time for dematerialization in Tempco… in our path toward digitalization we’ve taken a step forward by eliminating all the documents stored in our archives for the past 12 years.
In the sign of saving and recovery, heat recovery and not only, we’ve looked for a green way to recycle the whole amount of paper that was coming out of the paper shredder. We finally found a farm, the Farm Besana, that takes care of animals with respiratory disease due to hay using paper strips as bedding.
The paper bedding is eco friendly, absorbent and doesn’t generate dust. It is the ideal solution for horses with respiratory issues, and a valid and economic alternative to de-dusted hay.
A nice example of circular economy, don’t you think?
The beautiful horse pictured here is called Egano 7 and is allergic to hay, so that it must be fed only with de-dusted e wet hay.
Logarithmic mean temperature difference in heat exchangers selection
LMTD stands for Logarithmic mean temperature difference, being the logarithmic average of the temperature difference between the hot and cold feed on primary and secondary end of a heat exchanger. The value is fundamental for the calculation of the thermal exchange surface of a heat exchanger.
The LMTD is a crucial value also for the selection of the kind of heat exchanger most suitable for a certain application. Thermal transfer between two fluids presenting a short temperature gap is indeed very slow, while it will be much more faster and efficient in case of steam at 130° C to heat up cold water to a temperature of 70° C, for example. For the same reason, heat recovery is much more efficient having a small quantity of water at very high temperature instead of a lot of water at a mild temperature.
Plate heat exchangers allow to work with very narrow log mean temperature differences, thanks to possibility to work with countercurrent fluids and with turbulent flows, achieving high thermal exchange rates. Thermal transfer rates of shell and tubes exchangers are instead lower, thus requiring a higher LMTD. The Log mean TD is therefore even widened for air/water or air/steam finned pack exchangers, requiring very extended thermal transfer surfaces.
In general, the logarithmic mean temperature difference is inversely proportional to the thermal transfer surfaces. Even a half degree of difference has a strong impact on the heat transfer surface and the calculation of a heat exchanger, thus on its cost.
In Tempco we’re are willing to provide you some example of this kind of calculations!
Cooling of soda solution in oil & gas depuration process
We have recently realized an interesting application for the cooling of soda caustic solution employed in the separation and purification process in oil & gas facilities. The system employs a plate heat exchanger served by a chiller, that produces nonfreezing solution at the temperature of 0° C employed for the cooling of a caustic soda solution at 4%. The soda solution comes from the depuration process of the condensations of the petrochemical plant, with an inlet temperature in the plate heat exchanger of approx 45° C and outlet temperature of 25° C.
The treatment of condensations in an oil & gas plant is achieved using a bipolar cation and anion-exchange resins membrane process, that removes the ions present in the condensations cooled down at 45° C, in order to avoid possibile pollution by hydrocarbons. The exhaust resins are then regenerated with solutions of sulphuric acid and soda at 4%.
The heat exchangers has titanium plates, ensuring corrosion resistance due to possible presence of chlorides concentrations. The thermal power capacity is 500 KW, and all the connecting pipes are mixed rigid and flexible, in order to allow easy installation operations on-site.
The chiller provides the heat dissipation of the thermal energy removed from the soda solution, and must ensure 365/24 operations. The system is thus equipped with redundancy, with multi-compressor and multi-circuit, avoiding interruptions of the depuration process even in case of partial fault. In addition, the chiller has been sized for the most challenging summer design conditions, to guarantee the maximum efficiency in all variable weather conditions in winter/summer. A step regulation allows to adjust the power capacity to the season and to the effective thermal need required.
First start-up of a thermoregulating unit
The initial start-up of a thermoregulating unit is a very delicate monent, on which many customers ask for our support.
Industrial thermoregulation units by Tempco are supplied completely tested and checked. Once on-site, the units must be filled with the working fluid and started-up, and this operation is crucial for the safe and optimal functioning of the units.
The filling is indeed a very delicate step. In case of water or pressurized water as working fluids, the operation is simplified because water easily flows within the hydraulic circuits, giving no problems related to air bubbles. The operation becomes more delicate with diathermic oil thermoregulating units: the heat transfer oil has indeed a high viscosity, capturing and holding air bubbles.
It seems a trivial tip, but the very first thing to do proceeding in the first start-up of a thermoregulating unit is to check the rotation direction of the pump. This is important for two main reasons, the first being to ensure the correct functioning of the unit to achieve maximum efficiency, and then because a wrong pump rotation direction can damage the spring of mechanical seals of the pump.
Let’s then start filling up very slowly the unit, taking care of completely eliminate the air within the hydraulic circuit. Once the air is completely removed, is it possible to proceed with the first start-up of the thermoregulating unit, turning on the pump and checking the pressure indicator on pump delivery. The pressure indicator must be stable, indicating the nominal project value of the working pressure of the pump. Otherwise, if the indicator is shaking, it means there is still some air inside the circuit, that must be removed. The cycle must be repeated until the pressure is completely stable.
Once the air bubbles are totally removed, the temperature can be raised, setting an lower set point on the thermoregulator compared to the nominal final working temperature, checking that the pressure indicator is stable. The operation must be repeated until the final working temperature is reached.
The first start-up of a complicated industrial thermoregulating unit working with diathermic oil can even take a whole working day, but it’s very important to carefully achieve it. In particular, the first heating up run must be done gradually and very slowly, to ensure that there is no air bubbles within the hydraulic circuit, avoiding serious damages on the mechanical components of the unit, such as mechanical seals and heating resistances.
Brazed plate for renewable and electric vehicles
Talking about brazed plate heat exchangers, the new R series of heat exchangers offers heat transfer efficiency increased by 10%, and is optimized for applications in heat pumps and HVAC systems. Brazing material is copper, for a maximum working pressure in a range of 30-45 bar and maximum working temperature of 200° C.
The BPHE are available with two formats, with maximum number of plates of 120, available with different combinations of plate pattern, H, L or M.
The application fields are various, starting with HVAC systems and cooling and heating in industrial processes, such as machining centers and machine tools and plastic injection and extrusion systems. Especially interesting are the applications in the field of renewable energy, for example in gear boxes and hydraulic units in wind power generation and as evaporator, condenser and heat recovery in cogeneration and ORC plants. But also in transportation, not only for motor oil cooling in engine systems but also in battery cooling systems in electric vehicles, cars or buses.
Brazed plate heat exchangers, copper or nickel?
Brazed plate exchangers are a particular kind of plate heat exchangers that can be employed in applications with high pressures and a wider range of temperatures. This is due to the peculiar manufacturing process involved, that gives brazed plate heat exchangers a high mechanical resistance: plates in this kind of exchangers are made of cold-pressed stainless steel, and during the assembly of the heat exchanger the plates are piled in top one of each other with cold-pressed foils of copper or nickel between them.
The plate heat exchangers is then placed in a vacuum furnace where, at high melting temperatures respectively for the copper or nickel, the two metals melt, flowing for capillarity in the contact points welding them. All the brazed plate exchangers are checked with hydraulic pressure test, ensuring there are no pressure drops and to eliminate the defective ones.
When is better to choose copper vs. nickel? The selection must consider two factors, the need to work with corrosive fluids and the pressure level involved in the application. Copper is indeed an excellent material, but it is not compatible with steam containing amine and ammonia, being corrosive on the metal and leading in a short time to leaks and pressure drops.
A copper brazed plate exchanger on the contrary can stand pressures up to 30 bar and more, while a nickel brazed exchanger offer lower working pressure limits, 15 bar for a standard version and up to 25 bar for special versions. On the other hand, nickel is corrosion resistant to aggressive fluids that can cause corrosion to copper.
Dimple jacket exchangers in a seaport
We have developed last year an application for the dissipation of the heat produced by heat pumps, using TCOIL dimple jacket exchangers immersed in the Lake of Como. After less than a year, we are working on a new similar application that is now transferring us from the lake environment to the sea.
The solution employing TCOIL dimple jacket heat exchangers is indeed perfectly suitable for another customer, who requires the cooling/heating of water serving heat pumps in a seaport in the Italian Liguria region, using the presence of sea water. The customer at the present employs traditional plate heat exchangers, that due to the presence of sand and an inefficient filtration system used to get often clogged, leading to conditioning/heating problems of the connected equipments.
The solution developed and designed by Tempco consists in two batteries of TCOIL exchangers immersed in the waters of the seaport, manufactured using chloride resistant materials, I.e. SAF 2507 (duplex), avoiding corrosion issues with the dimple jacket exchangers operating in continuous contact with the sea water.
The installation is planned for July 2019, just in time to the start of the summer season. On a second step, we will also supply the customer further additional heat exchangers, for the revamping and energy consumption optimization of the plants.
Fouling factor in heat exchangers
More about heat exchangers, and in particular let’s face the topic of fouling factor in heat exchangers. This is a relevant topic in order to ensure the proper thermal transfer efficiency in exchangers, as I’m often asked about it. Fluids flowing inside heat exchangers can indeed contain particles that lay down in sediments in the long term, sticking on heat transfer surfaces and lowering the exchanger’s thermal efficiency.
The fouling factor is a sizing up coefficient to be applied while engineering a heat exchanger. In fact, a higher margin must be accounted in the sizing of a heat exchanger, counteracting the fouling on heat transfer surfaces due to the settling of fouling particles.
The evaluation of the coefficient relies on the kind of flowing movements involved in the heat exchangers, impacting the quantity of particles that can buildup on thermal transfer surfaces. The fouling factor then varies depending on the kind of heat exchanger, being different for a shell & tube exchanger or a plate heat exchanger. The effective fouling factor values for a plate heat exchanger are ten times lower than the ones applicable to shell & tube heat exchangers, because fluids in a plate heat exchanger have a much more turbulent flow.
A turbulent flow of the fluid within plate heat exchangers allows to drag the particles that have the potential to settle on heat transfer surfaces, thus requiring a lower oversizing coefficient of the exchanger. Another reason is represented by the construction of the kind of heat exchanger itself: a shell & tube exchanger, once it’s manufactured, cannot be expanded, while a plate heat exchanger allows to vary and increase the number of plates, boosting its thermal transfer efficiency in case of fouling fluids or different operating conditions compared to design parameters.