HRS helps AD plant tap into additional heat from existing CHP

Operators of anaerobic digestion (AD) plants know how important it is to optimise energy use across all stages of the process. That is why many recapture as much heat as possible for reuse elsewhere, including from the hot exhaust gases generated by the combined heat and power (CHP) engines which turn the biogas from the AD plant into useful heat and electricity.
Heat exchangers used for exhaust gas heat recovery need to be particularly robust in order to cope with the physical and chemical stresses imposed on them from the exhaust gases which are both hot and corrosive. HRS Heat Exchangers were recently asked to install just such a unit.
An AD site, belonging to one of the leading waste management companies in the UK, transforms some 45,000 tonnes of food waste from domestic and commercial sources into renewable electricity and high value digestate biofertiliser. From the beginning the plant had been designed to be as efficient as possible and included exhaust gas heat recovery. However, when the original heat exchanger fitted to the exhaust system failed after just a few years of operation, the client approached HRS to provide a more robust and reliable replacement.
The ideal solution was an HRS G Series gas cooling heat exchanger: a complete stainless steel multi-tube heat exchanger specifically designed for exhaust gas cooling and thermal recovery. The hot exhaust gases flows through the interior tubes of the heat exchanger while the service fluid, in this case water, flows though the surrounding shell. The use of stainless steel is a key factor in the longevity of the G Series and rapid corrosion of the original carbon steel unit was one of the reasons for the original’s failure.
Other design features of the G Series also increase its operational life as Matt Hale, International Sales & Marketing Director at HRS Heat Exchangers, explains: “All HRS tubular heat exchangers include bellows in their design to allow for thermal expansion. The original heat exchanger we replaced was exposed to significant thermal stresses which contributed to its early failure.
“You also need to consider the condensation which can occur when the hot gas meets the tube plate and cooling begins. The resulting condensate is acidic and can be extremely corrosive, so the HRS G Series includes drains in the header to allow this condensate to be removed, as well as a hatch to allow for manual cleaning and inspection.”
As an operational plant, it was important to keep downtime at the plant to a minimum during the installation of the new unit. HRS manufactured the new heat exchanger to the same eternal dimensions and used the same connections as the original. This enabled a straightforward installation in just a few hours without any pipework modifications, with the installation being carried out just eight weeks after design approval.
In operation the new G Series heat exchanger cools the exhaust gas from ~530oC to ~320oC and the heat recaptured from the process is used in the AD facility and to provide hot water around the site. Since installation the HRS G Series heat exchanger has performed so well that HRS has been asked to quote for the replacement of another unit which is used to treat the digested sludge from the plant, with an HRS DTI Series unit.

Product-to-product heat recovery

Wastewater, sewage, effluents and sludge are useful sources of energy with the potential to heat (or in some circumstances cool) other products or materials in industrial processes. The DTR Series of double-tube heat exchangers from HRS is designed to maximise direct (product-to-product) energy recovery from such low viscosity materials, allowing valuable heat to be recaptured before the effluent enters final treatment or is discharged to the environment.

Where biological water treatments are employed, it may be necessary to reduce the temperature of the effluent before treatment. For aerobic decomposition or other biological treatments, temperatures between 25 and 35˚C are recommended; with activity ceasing above 50˚C. However, the temperature of discharged cooling water is often around 40˚C; while work in Switzerland suggests that domestic wastewater typically has a temperature around 20˚C and rarely falls below 10˚C. Capturing the effluent closer to its source can result in higher temperatures.

Making use of any available heat is good for both your pocket and the environment, reducing the energy required for heating, with a corresponding drop in greenhouse gas emissions. Discharging water which is closer to ambient temperatures is also much better for the wider environment. The series has been designed specifically to use low viscous products (or waste streams) as the heating (or cooling) medium. The DTR series is perfect for direct sludge to sludge heat recovery and environmental industry heat recovery.

The tube-in-tube design means that the DTR series copes well with fluids that contain particles, without the worry of blockages impeding the flow of product or heating medium. Special stainless steel corrugated tubes are used to increase heat transfer and reduce fouling, making the DTR Series more efficient than similar smooth tube heat exchanger designs.

The inner tube of the DTR Series is removable for inspection, cleaning and maintenance, meaning that both the tube and shell sides can be inspected and cleaned, while the corrugated tube technology that HRS is so well known for improves heat transfer, yet reduces potential fouling compared to standard smooth tube heat exchangers. This allows the product or waste stream to run in both the inner and tubes. It also allows for easier and faster cleaning, so overall there is less operational downtime, even with high fouling products.

For large installations, multiple units can be interconnected and mounted in a frame, and a range of options, including thermal insulation and cladding in materials including stainless steel are available.

Debunking the myths about food pasteurisation

Pasteurisation has been established as a key method of destroying pathogenic bacteria in the food and drink industry since is invention in the middle of the nineteenth century, although the origins of heating wine for preservation go back to China in the 1100s. However, as food and drink processing becomes more complex and food chains longer, the importance of pasteurisation has increased.

At the same time, the technology has also improved, with developments in the equipment used for both  for High Temperature, Short Time (HTST) and Low Temperature, Long Time (LTLT) methods. While simple plate heat exchangers may still be suitable for the pasteurisation of simple fluids such as milk and fruit juices, more textured and viscous products, such as cooking sauces, creams and curds will require different solutions in order to maintain their quality and texture. Here we dispel seven popular myths about food pasteurisation

Myth 1: Pasteurisation is expensive
While the exact costs will vary with each installation, there is no doubt that there is a capital cost to pasteurisation. However,  compared with the potential losses due to food spoilage, or worse, a food safety incident, these costs are insignificant. In the US, the costs of recalling food products have been shown to average $10 million, before accounting for brand damage. Closer to home, microbial contamination resulted in 59 product recalls in Australia between 2014 and 2016. Furthermore, Food Standards Australia New Zealand reports that  Listeria monocytogenes, Salmonella and  E. coli are the three micro-organisms most commonly associated with microbial food recalls in Australia, while those products most recalled are meat and dairy items.

Against these potential costs, the capital cost of a corrugated tube heat exchanger based pasteurisation system is a sound investment. Alongside the capital costs, the running costs of a pasteurisation unit need to be considered. Heat exchangers and  pasteurisation units made by HRS Heat Exchangers are designed to reduce fouling and maintenance, while our wide range of heat recovery options mean that energy costs are kept to a minimum.

Myth 2: Pasteurisation is too complex
Pasteurisation itself is a relatively simple process. It requires that a material is held for a certain time at a certain temperature in order to kill micro-organisms. There is no doubt that pasteurisation adds an additional step into the overall manufacturing process, but if well-designed it should not slow down throughput or place additional management burdens on the plant. The use of continuous pasteurisation systems mean that the process is simple and the potential for product damage or change in quality is minimised.

Myth 3: Pasteurisation is only suitable for simple fluid materials
Pasteurisation can be used on a wide variety of liquid and semi-liquid materials. While simple Newtonian fluids will be the easiest to work with, and can often be effectively pasteurised with a simple plate heat exchanger, there are solutions for almost any material. HRS innovations, such as the use of corrugated tube and scraped surface heat exchangers, means the company can deal with anything from viscous fluids requiring gentle handling or with low rates of heat transfer, to complex mixtures, such as curd cheese, which could otherwise foul the heat exchanger, reducing thermal efficiency and requiring regular cleaning and  maintenance.

Myth 4: Pasteurisation requires a lot of energy
The amount of energy used in food pasteurisation is highly variable depending on the process used, the nature of the material being treated and the heat exchanger used. The bulk of any energy requirement is used to raise the temperature of the foodstuff.

Traditional pasteurisation units simply dump this heat afterwards, meaning they are incredibly wasteful and inefficient. Where possible, HRS heat exchangers recapture the heat and use it again, making them up to 70 per cent more efficient than some traditional systems.

Myth 5: Pasteurisation equipment is high maintenance
The use of corrugated tubes, together with integrated cleaning-in-process (CIP), minimises the amount of fouling and therefore the amount of cleaning necessary to maintain the efficiency of HRS pasteurisation systems. The careful design of static tubes also helps keep down production (and therefore purchase) costs.

Myth 6: You cannot pasteurise viscous fluids
Subjecting viscous and non-Newtonian fluids, such as cooking sauces, to shear stress during the manufacturing process can damage  the quality and texture of the material, which may preclude the use of certain designs of heat exchanger for pasteurisation. However, by choosing a system such as the HRS Unicus scraped surface heat exchanger, which prevents fouling while maintaining  relatively low pressure, such unwanted effects can be overcome.

Myth 7: Pasteurisation is the same as sterilisation
Unlike sterilisation, pasteurisation does not completely eliminate micro-organisms which may be present in the foodstuff. Pasteurisation reduces the microbial load by a significant factor (for example by 5-logs), which in normal circumstances reduces contaminating pathogens to a level at which they do not pose a hazard. Pasteurisation need not be overly onerous or detrimental to the quality of the product. Certainly, with the correct choice of equipment, pasteurisation does not need to have a negative effect on plant throughput or efficiency and a well-designed system incorporating heat regeneration and corrugated tubes should enhance the overall facility, helping to add flexibility to your business.

A heat exchanger Furphy worth believing

Furphy Engineering, a company whose name has become part of the Australian lexicon, now has a new reason to feel unique. It is the only local manufacturer using laser welding to manufacture ATEX plate heat exchangers. Matthew McDonald writes.

During World War I, water carts made by Shepparton-based Furphy Engineering were used to deliver water to Australian troops.

Like today’s water coolers, the carts became places to meet and talk. Of course, talk has a habit of leading to gossip, so stories heard around the water carts came to be treated with scepticism. And you guessed it, they became known as ‘furphies’.

The rest is history.

Today, stainless steel tanks and vessels are Furphy Engineering’s main area of business. The company counts dairy companies, chemical companies, and breweries amongst its many and varied customers across Australia.

Manufacturers Monthly recently caught up Managing Director Adam Furphy (a fifth generation descendant of the company’s founder).

He explained that one of the standard features for many modern tanks and vessels, particularly those used in food and beverage applications, is what’s known as cavity plate, dimple plate or cooling jacket. ‘Dimple’ refers to the uniformly bumpy surface of the plate.

“It’s essentially an outer skin on the shell of the tank that is formed such that there’s a cavity between the outside of the tank and a second wrap of material and through that cavity glycol or cooling fluid can be run to cool the tank,” he said.  Alternatively a heating liquid can be used to heat the product inside the tank via the same process.

It provides a way for wine makers, dairy factories, brewers and so forth to keep their products at the right temperature to optimise their processes.

Furphy Engineering is the only company in Australia which uses a laser welding technique to manufacture Advanced Thermal EXchange (ATEX) dimple plate.

In the case of tanks and vessels, the ATEX Plates are described as single embossed whereby only the thinner outer skin of the plate is deformed when the welded plates are pressurized.

“That’s the way we’ve been doing the majority of our applications to date but recently we’ve become more interested in what we’d call double embossed ATEX applications,” said Furphy.

He explained that, unlike the single embossed material created for tanks and vessels, double embossed ATEX plates are dimpled on both sides and are therefore suitable for complete immersion in the medium to be heated or cooled, doubling the heat exchange surface area. Plates can then be banked together using manifolds and tailored to fit in an existing installation, providing a highly efficient and customisable immersion plate heat exchanger.

According to Furphy, the applications for this are far reaching. “We’ve seen inquiries for regulating key product temperatures, keeping waste water below regulatory requirements; or to simply cut costs by turning waste heat into pre-heat. ATEX allows us to tailor solutions to an even greater range of these heat exchange problems that are everywhere in industry,” he said.

The benefits

According to Stephen Lawrence, an R&D Consultant for Furphy Engineering, heat exchangers manufactured using ATEX Plates are also useful from a thermally sensitive point of view. They lend themselves to use as falling film plates in chillers and evaporators which are particularly suitable for delicate products used in food and chemical industries.


“Making [those products] is difficult with traditional heat exchangers because you get a rather short dwell time which means you have to transfer a lot of heat from the product to the heat exchanger very quickly and thermally sensitive products like that struggle,” Lawrence told Manufacturers’ Monthly.

In contrast, using ATEX heat exchangers, the material flows down the outside of a long plate, allowing more time for it to perform the heat exchange.

“This, in turn, is more delicate on the product and gets the end result more effectively,” said Lawrence.

According to Furphy, the versatility of the technique is another advantage. “Any shape you can think of we can make in ATEX plate,” he said. “…shapes you couldn’t do before in terms of heat exchange become possible.  Examples are pipe work and gas ducting.”

In addition, the heat exchangers are made with food grade stainless steel, and are easy to clean and maintain.

Furphy pointed out that laser welded dimple plate is currently much more widely used in Europe than in Australia. He sees a gap in the market which his company is now seeking to exploit.

He offered an explanation as to why Australia is lagging behind in this area.

“A large number of the applications we’ve seen relate to energy saving of some kind,” he said. “That seems to me to be the real driving force behind the use of the products. Not all of it, but a significant feature.”

“The Europeans are more dialled into this because they’ve had a longer period of high energy prices.”

In contrast, he said, high energy prices and the need to reduce energy usage are relatively new to this country.

 “By and large in Australia industry is still getting its head around what possibilities exist and what potential there is to reduce their energy costs utilising some of the waste heat streams that perhaps exist on their existing sites,” he said.

Pointing to the example of a northern Victorian laundry operation which was able to cut its water usage by 20 per cent and its gas bill by 14 per cent by installing an ATEX heat exchanger, Furphy said the savings are there for those who want them.

Sounds like a Furphy worth believing.