Westcome heat exchange
Why you should invest in a Westcome heat exchanger
Most heat exchangers are designed for heat exchanging low viscosity media whereas Westcome heat exchangers have been developed specifically to exchange heat from sludge, slurry and other biomass with high dry matter content and with a dry matter composition in which energies are difficult to move.
Westcome heat exchangers are the only heat exchangers on the market designed as single-tube heat exchangers where heat is exchanged directly from high viscosity flows in a direct counterflow exchange, such as slurry / slurry, without an additional circuit to transport the heat energy between the two circuits.
All Westcome heat exchangers are designed according to the tasks to be solved and are available in the lengths, widths and heights that match the space available. Difficult access will not hinder installation of the product.
Purpose-built
Westcome heat exchangers are designed for each task and thus ensure maximum yield and minimum operating costs based on:
- Low pressure loss
- Constant high efficiency
- Design without seals
- Same cross-section throughout the heat exchanger
- No cleaning
- Cleaning without stoppages
- No fouling
- No maintenance
Design and construction
The carefully prepared design and construction of the Westmore heat exchanger has several advantages, of which the following should be highlighted:
Low pressure loss / low energy consumption
The pressure loss across the heat exchanger is important to the power consumption for the operation of the sludge pumps just as pump wear is reduced which results in longer service lives at low pressure losses.
Westcome heat exchangers are designed for low-rate operation, typically 0.3 m/s, which involves a low-pressure loss compared with the pressure loss of other heat exchangers, which often have flow rates in excess of 1.0 m/s.
If the flow rate is changed from 0.3 m/s to 1.0 m/s, power consumption of the sludge pumps increases by >350%.
Constant high efficiency
A Westcome heat exchanger maintains its high efficiency throughout its service life and has no drop in efficiency due to gradual blockage as the operation mode includes cleaning of the heat exchanger during operation.
Compact and flexible
A Westcome heat exchanger is customised and tailored to the job.
Lengths, widths and heights are available which are fully adapted to the conditions existing at the installation site.
The heat exchanger is available with efficiencies as requested, if required up to 75%.
Sludge / sludge and sludge / water exchangers are also available in one single cabinet.
The Westcome heat exchanger is delivered as standard in an insulated cabinet for indoor installation to prevent heat emission to the surroundings but is also available in a cabinet for outdoor installation.
The cabinet for heat exchanger is made in 0.8 mm brushed stainless steel plates with 25 mm polystyrene insulation on the inside for indoor installation.
No seals
A Westcome heat exchanger is designed completely without seals as an all-welded design which means no costs for replacing seals.
The design of the Westcome heat exchanger without seals eliminates the risks of deposits in rough areas in connection with the seals.
Same cross section
The tubes throughout the exchanger have the same cross section: The sectional area remains the same, even in bends, which means that the flow rate remains the same. The patented bend design forms an additional active heat transferring part of the heat exchanger.
Cleaning and operation in sewage treatment plants
Time and manpower for cleaning the exchanger is rarely required with a Westcome heat exchanger which enables cleaning during operation. This only requires the installation of a valve setup to change circuits (hot to cold and vice versa) and flow directions at preset intervals (typically once a day) or as required.
Changing circuits between the cold and hot sides removes grease, etc. which may deposit on cold surfaces, and which is removed before it accumulates and causes problems.
In some process where the process is demanding flow with there must be dealing with
Valve setup with 2 x 4 valves / two-way motor-operated valves to change flow direction and side.
When the recommended valve setup is installed, manual cleaning of a Westcome heat exchanger will usually not be required at the sewage treatment plant. However, if a blockage occurs due to unforeseen events, the Westcome heat exchanger is designed for easy cleaning where staff or surroundings will not come into contact with the contents in the heat exchanger.
The Westcome heat exchanger has connectors at both ends of each exchanger channel so that each exchanger tube can be inspected and any blockages or foreign bodies can be flushed out.
One or more exchanger tubes can be flushed at a time. At the opposite end, the discharge hose is connected to lead the flush water to a drain, preventing pollution of the surroundings.
Specific problems in sludge heat exchange
Four problems, may occur in connection with biomass heat exchange.
- Layering of the medium
- Fouling due to temperature differences
- Sand deposits
- Deposits due to struvite precipitates
Westcome has solved these problems as follows:
Layering of the medium / laminar flow
The high viscosity of the sludge / biomass requires agitation of the medium during the heat exchange. As sludge is also a poor thermal conductor, agitation is crucial to bring the sludge into contact with the heat-conducting surface and prevent the sludge mass from staying laminar and not turbulent.
A high flow rate helps solve these issues in other types of heat exchangers, but it also involves a high-pressure loss.
In contrast with other types of exchangers, agitation in a Westcome heat exchanger is not carried out by means of a high flow rate but by means of baffles that affect the sludge’s ability to rotate thus ensuring mixing.
Agitation occurs at very low flow rates.
Accumulation of sand in the heat exchanger can be prevented at flow rates as low as 0.3 m/s.
To prevent laminar flows in the exchanger channels, baffles have been integrated at regular intervals throughout the heat exchanger. The baffles have been designed so that they do not cause any measurable increase of the counter pressure through the heat exchanger, and they do not depend on any flow direction in the heat exchanger but have the same effect, irrespective of the direction in which the sludge meets the baffles.
Due to the design of the channels, the sludge will not only rotate when passing the baffles but will also be affected so that the core of the sludge is moved to the “outside” of the sludge thus ensuring the maximum heat transfer between the hot and cold sludge in the two channel flows.
Fouling due to high temperature differences
During heat exchange, the temperatures of the hot and cold sides differ, the so-called mean difference temperature.
In the Westcome heat exchanger, the cold and hot flows cross from side to side as shown below. This achieves the same mean difference temperature throughout the heat exchanger.
Due to the low mean difference temperature in the heat exchanger, no fouling will occur on the insides of the heat exchanger which may occur in the event of large temperature differences between the insides of the heat exchanger and the medium for heat exchange.
Fouling means deposits and will reduce the efficiency of the heat exchanger when contact between the cold and hot sides is reduced.
Sand deposits in the heat exchanger
In areas where the rate is lowered, sand will usually be deposited in heat exchangers and piping.
Traditional heat exchangers try to avoid this issue by using a high rate (0.8- 1.0 m/s through the heat exchanger) and then create turbulence to prevent the sand from depositing.
A low rate is not a problem in the Westcome heat exchanger. Sand deposits are avoided by creating turbulence through a design with regularly placed baffles throughout the heat exchanger.
See “Layering of the medium” above.
Deposits due to struvite precipitates
Struvite precipitates may be a problem when certain conditions exist in the sludge / biomass and are often seen in heat exchangers using sludge from digestion tanks in sewage treatment plants. Struvite precipitates are the result of supersaturation and happen in a specific pH area and in connection with temperature drops in the biomass. At biogas plants, struvite precipitation is even more marked as the contents of ammonia and phosphorus are many times higher than at sewage treatment plants.
Once precipitation has begun, the risk of impending blockage of pipes or heat exchangers is large as the deposits attach more easily to rough and uneven surfaces. Cleaning of heat exchangers where struvite precipitates have become a problem is usually carried out by separation and manual cleaning or by cleaning in place by using acid to remove struvite.
Cleaning and operation of the Westcome heat exchanger at biogas plants
The Westcome heat exchanger is designed without gasket, and we consider maintenance costs to be non-existing.
To clean unintended injection of particles, the heat exchangers can be cleaned through the end plugs of the exchanger pipes without staff or surroundings encountering the contents of the heat exchangers.
To keep the heat exchangers clean and free from struvite, polymer can be injected in the hot outgoing, degassed mass from the digestion tanks.
The Westcome heat exchanger is designed specifically for heat exchange of high-viscosity flows, such as slurry, sludge and other biomass with high dry matter content.
Westcome heat exchangers can transfer energy in a direct counter flow, such as sludge to sludge, sludge to water or water to sludge. Given the direct transfer between the two media, efficiency increases significantly compared with the use of flow from other sources.
When lowering the temperature of slurry and biomass in heat exchangers, struvite precipitates inside the heat exchanger and deposits on the inside of the heat exchanger.
This struvite precipitation forms a hard crystal layer on the inside walls of the heat exchanger which gradually increases the pressure loss inside the heat exchanger just as the heat transfer between the two flows in the heat exchanger is reduced.
Struvite precipitation can be prevented by injecting Kem Guard 5872 polymer from Kemira at a ratio of 20 ppm / m³ degassed hot biomass.
The Westcome V3 heat exchanger has been designed to ensure that the sectional area remains the same in the heat exchanger from start to finish. This means that there are no “warm” or “dead” zones in the heat exchanger as agitation is carried out by baffles, even at low flow rates.
Westcome heat exchangers vs. heat pumps
Combined with heat pumps for the delivery of process heat to the plant’s reactor tanks, sanitation, etc., the Westcome heat exchanger can deliver this energy from a plant, which wants a plant COP of 8 – 14, depending on the plants’ temperature sets.
Westcome heat exchangers vs. heat pumps
Combined with heat pumps for the delivery of process heat to the plant’s reactor tanks, sanitation, etc., the Westcome heat exchanger can deliver this energy from a plant, which wants a plant COP of 8 – 14, depending on the plants’ temperature sets.
Layout drawing: 1. sludge / sludge exchanger 2. sludge / brine 3. brine / sludge
Brine circuit is available with a split flow = 2 – 4 x m³ sludge / h = < Pressure drops and > efficiency of VP (see description in process heating pdf)
Patents: The Westcome heat exchanger is patented under patent no. DK 178 079/ EP 3 037 766 A1
Warranties: The heat exchanger is covered by a 5-year warranty from the start-up of the plant. This warranty covers all types of breakdowns or wear which are not due to the addition of aggressive substances to the sludge or momentary and / or pulsating exceeding of the operating pressure, regardless of these do not exceed the specified operating pressure and are otherwise operated in accordance with the installation instructions.
Expected service life: 15 – 20 years.
Maintenance costs: As the heat exchangers are made without seal, we consider maintenance costs to be non-existing.