In general, the more viscous the fluid, the lower the heat transfer is. This means that very viscous fluids require a very large heat transfer area. Scraped surface heat exchangers vigorously mix the fluid, which helps to move the fluid to and from the heat exchange surface. This increases heat transfer rates, so the total area required for heat exchange is reduced.
For difficult heat transfer applications, with high viscosities and where fouling can become a problem, the preferred option is a scraped surface heat exchanger. Scraped surface heat exchangers keep heat transfer high and the heat transfer surface is constantly cleaned.
HRS offers two technologies for scraped surface heat transfer: the patented HRS Unicus Series which reciprocates and R Series which rotates, each designed for specific needs.
Increase in processing of viscous products from food, pharmaceuticals to environmental require advanced technology with good return on investment. Traditional methods used for evaporation, crystallization and high fouling applications are insufficient to meet industry demands for better quality, capacities and cost efficiency.
UNICUS heat exchanger is formed by a tube bundle inside a shell. Scraping elements attached to rods are placed inside each tube of Unicus. The movement of these rods is programmed from the control panel and powered by a hydraulic power unit.All inner tubes include moving bars that support the scraping and mixing elements, This unique design heat exchanger surface clean of fouling and agitate the flow to boost the overall heat transfer coefficient by action.(unlike conventional scraped surface heat exchangers that move in rotation).
Fouling During Heat Transfer
Fouling occurs when particulate or viscous matter sticks and degrades at the tube walls. Another form of fouling is crystallization where, due to cooling or increasing concentration, components in the fluid change to the solid state and deposit on the heat exchanger surface. These layers work as an insulator for heat transfer, causing performance to drop. UNICUS enables scraping of the heat transfer where fouling layers need removal to maintain high heat transfer in place. Scraped surface heat exchangers mix the fluid vigorously, which helps to move the fluid to and from the heat exchange surface. This increases heat transfer rates, so the total area required for heat exchange is reduced.
The patented UNICUS series is a scraped surface heat exchanger has been specially designed and developed to offer a solution for those difficult heat transfer applications, like evaporation, crystallization of chemical, food, environmental applications where product viscosity is usually high.
The UNICUS Series heat exchanger consists of three main parts:
The design is based on a traditional shell and tube heat exchanger with scraping elements inside each interior tube
The separation chamber: This space separates the shell and tube heat exchanger from the drive cylinder that moves the scraper bars
The cylinder: This part provides the energy that moves the scraper bars. The cylinder can be pneumatic (smaller models) or hydraulic (bigger models)
Units are 6 or 3 meters long and it has very few spare parts (there are no mechanical seals, etc.) The design of the units is patented
The reciprocating movement of the scrapers mixes the fluid whilst cleaning the heat exchange surface. The Inner tubes are smooth and seamless with good internal surface finish
The heat exchanger can be drained after use
Component thicknesses and/or connection ratings may be varied for specific applications where large differential component temperature levels are likely to be experienced
A key component of the UNICUS Series is the seal that separates the inner tube volume from the separation chamber. The seal prevents leakage of the product to the exterior. Several types of seals have been developed depending on the application
Material of Construction
UNICUS can be designed and manufactured in various grade of tube and shell material as per process requirements. Materials: Shell side: AISI 304 stainless steel; Tube side: AISI 316L stainless steel Connections: Shell side: Flange; Tube side: clamp / flange External Finish: Satin or Polished: Product side: <0.8 microns Design conditions: Shell side: 10 bar(g) / 185°C; Tube side: 16 bar(g) / 185°C Scraping elements are manufactured in different materials like Teflon, polysulphone, peek, etc. in sizes of 1200 and 1800 or 3600. Scraping/mixing blades in PTFE and silicone (both FDA approved). Metallic blades are available for non-hygienic applications.
SCRAPING ELEMENTS & SEALS
Scraping blades are designed to be light, highly chemically resistant and thermally more efficient, thus reducing both weight and energy consumptions with an effective scraping action. They are combined with a silicon spring or peek segments to fit tightly to the tube surface. The design temperature is 165°C. The design pressure is 16 bar on the product side and 10 bar on the service side. Higher pressure ratings are available subject to a revision of material compatibility, component thickness and connection types.
DIN11851, ISO clamps, aseptic ISO clamps or sterile flanges on the product side and DIN11851, DIN2576 flanges or ISO clamps on the service side. Other couplings can be made available as required. The mounting is usually done on SS 304 skid frame. The units can be installed horizontally or vertically.
Two scraped surface heat exchanger solutions have been developed for different types of applications – UNICUS Reciprocating Scraped Surface Heat Exchanger & UNICUS Rotating Scraped Surface Heat Exchanger.
UNICUS can have series or parallel flow configuration depending on the application. It can work horizontally or vertically because the scraping is alternating. This allows the units to work at all flow rates without any limitation, regardless of the temperatures, program or product nature. Product flow can be in single or multiple pass.
UNICUS can have series or parallel flow configuration depending on the application. scraped surface heat exchanger solutions have been developed for different types of applications
It can work horizontally or vertically because the scraping is alternating
Product flow can be in single or multiple pass
Continuous improvements have allowed HRS Heat Exchangers to apply the UNICUS in a wide range of markets and applications. By increasing the stroke speed of the scraper bar we have been able to increase the heat transfer rates considerably. By adding new scraper types we have adapted to the difficulties that new products may present
The increased range of models available has made it possible to offer economic solutions for small to big duty applications. From food industry to environmental industry, from biomass to evaporation applications, the UNICUS series is a robust solution where other types of heat exchangers fail to deliver a good result
UNICUS Series models are available in versions containing just one tube, up to models with 80 tubes inside. This allows UNICUS Series models to have heat transfer areas between 0.7 and 100 m². A standard range of models up to 10 m² is available for hygienic food applications and other industrial applications, while the larger of models are tailored to final use.
UNICUS increases heat transfer coefficients and guarantees continuous heat transfer because there is no fouling of the heat exchanger walls
The reciprocating movement of UNICUS increases the mixing level
Reduction in the heat transfer surface and therefore a reduction in the cost of the unit with less materials
A variety of scraper blades are available so the blade can be matched to the product
The design of the heat exchanger allows hygienic or industrial construction
UNICUS is simple and economical to maintain
With the UNICUS it is possible to put multiple product tubes in the shell making it even more compact
UNICUS heat exchanger works close to zero fouling. The Heat Exchanger is always clean
Due to the patented self cleaning device the product channels are always clean so the unit works in the optimum condition for heat transfer at all times
Drastic reduction in production losses because there is no wasted time cleaning the heat exchanger
The heat exchanger is self draining allowing total product recovery
Shaft movement in compact length uses relatively less energy the Unicus has low power consumption, making it very cost-effective to run
UNICUS minimizes the shear rate and maintains particulate structure. The gentle movement of the scrapers allows the system to be used with delicate products, such as food products with whole fruit or vegetable pieces, without destroying the integrity of the product
It allows for gentle product handling since the shaft is moved back and forth once every six seconds and can be slowed down even further if required
As the scraper blades support the central shaft it is possible to make the heat exchange length as long as is required, with 6 m long units built regularly as standardvv
In continuous cooking applications, UNICUS reduces the cooking time by up to 15 times, maintaining the integrity of the food and achieving a home cooked taste
UNICUS scrapes the crystals from the heat exchanger wall
UNICUS is a perfect finisher, it will increase product concentration levels
UNICUS allows for a continuous evaporation process, reducing volume of industrial waste and recovering volatile components. UNICUS evaporates without CIP for long periods
The HRS R Series is a scraped surface heat exchanger designed for the most difficult heat transfer applications, for example where very high viscosities and highly fouling fluids need heat treatment.
Unlike the HRS Unicus Series, where the scraper movement is reciprocal, the HRS R Series technology uses a rotary scraper rod. This scraper rod can reach velocities up to 300 rpm resulting in very high levels of shear and mixing at the heat transfer surface; dramatically increasing the heat transfer rate.
In addition to the standard R series a heavy duty version is available. The HRS RHD Series has been developed for the more demanding applications with extreme viscosities. The RHD has all the features and benefits of the standard R Series but with increased motor size and scraping rods. Extra mounting supports for the scrapers and motor enable the unit to be used under challenging conditions.
The R and RHD Series has been developed for both hygienic and industrial applications. Each inner tube contains a scraper bar fitted with a helical screw which rotates at high speed and enhances flow through the tube whilst reducing pressure drop. In addition, the continuous scraping action eliminates fouling on the inner tube wall, ensuring that the heat transfer area is clean at all times.
The R and RHD Series are suitable for heat transfer applications on a wide range of products and applications: