GREASE TRAP WITH HEAT RECOVERY APPARATUS

Field of the Invention

The invention relates to a heat recovery structure placed around a heat source. In particular, the invention relates to the structural and mechanical arrangement of a heat recovery apparatus surrounding a heat-losing structure containing a target fluid, in order to recover a significant part of the heat lost by the target fluid.

Background to the Invention

Heat recovery from waste fluid is desirable. Some estimates have shown that an increase of 12°C in a heating fluid due to heat recovery could save up to 75% in heating cost. Heat exchangers are widely known in almost every industry. Heat exchangers transfer heat between two fluids (liquid or gas) through a heat conducting barrier which prevents the mix of the two fluids flows.

The double pipe heat exchanger is one of the most basic but versatile members of the heat exchangers family. In its simplest form, a double pipe heat exchanger has one pipe concentrically placed inside a larger pipe. In this case, the wall of the inner pipe acts as the conductive barrier. The outside flow passes over the inside flow, which will provide heat transfer through the conducting wall. The double-pipe heat exchanger can be used in parallel flow or in counter flow (fluids moving in opposite directions, for better heat transfer). Double-pipe exchangers can freely expand and have a simple and solid construction. Similar structures are often referred to as hairpin, jacketed pipe, and pipe- in-pipe exchangers.

The approaches to heat recovery could be classified as:

• Internal recovery: heat is transferred through a device (for example, a baffle) inserted into the heat losing medium.

• External recovery: heat is transferred through a device surrounding the heat losing medium.

Although internal heat exchange structures recover some of the heat, a significant portion of the heat is always lost to the surrounding environment, reducing the effectiveness of the heat recovery. Simple external structures for heat recovery are typically pipe structures, which partially coil around the heat source. These coils are often placed along the pipes which contain a running fluid (not necessarily a captive fluid), which often barely touches the walls of the pipe. Much of the heat remains with the running fluid and is subsequently lost. This is particularly obvious in the case where the fluid is a liquid, as the liquid accumulates in certain regions only, driven by gravity. The accumulated liquid performs a specific function in p-traps, preventing odours. The accumulated liquid is also required for the appropriate separation of grease, sand and other liquids inside grease traps.

US Patent No. 8,603,336 describes a heat exchanger disposed in a tank, wherein the heat exchanger comprises a substantially vertical outer surface of spaced apart tubes; a fluid flowing through the heat exchanger; an inlet and outlet for the fluid that are connected to one another by at least one flow conduit, the outer surfaces of which flow conduit form the outer surface of the heat exchanger. The fluid flows in a preferably turbulent manner through the flow conduit from the inlet to the outlet. In order to keep the flow rate low and the temperature difference between inlet and outlet high, the flow conduit typically has a small hydraulic diameter and is long. The fluid flows along inner surfaces of the walls and the wastewater flows along the outer surfaces of the walls.

European Patent Application No. 16154935 describes a grease trap with at least one heat exchanger disposed therein. The heat exchanger comprises piping arranged in a tortuous fashion, typically in a coiled or raster pattern, that includes an inlet, which is connectable to a source of a heat transfer medium, for example a cold water supply, and an outlet, which is connectable to, for example an additional apparatus, such as a boiler or a storage receptacle such as a water tank. The heated heat transfer medium is fed to the boiler, where the energy required to heat the heat transfer medium to an operating temperature is reduced because of the heat supplied from the grease trap. The heat exchanger is inserted within a receptacle built into the heat trap.

DE 3045740 A describes a heat recovery apparatus comprising a housing, an inlet, an outlet, an outer wall and an inner wall accommodating a heat recovery fluid and also defining a central core accommodating a waste fluid. CN 108507395 A also describes a heat recovery apparatus comprising a housing with an inlet, an outlet, an outer wall, an inner wall in the form of a conduit defining a central core. Some of the problems with the heat exchangers of the prior art is the non-optimized interfaces for heat exchange; the complexity of manufacture; and the heat loss through external walls.

It is an object of the subject application to overcome at least one of the above-mentioned problems.

Summary of the Invention

The invention comprises a simple external wall structure to recover the heat from a container of fluid, for example, drains, sewers, and grease traps. In particular, the pipe or container of interest includes the section of the drains, sewers, or grease traps where the fluid is captive. The invention can be used in grease traps.

The invention overcomes the problem of heat loss from fluid-containing structures by substantially encapsulating a relevant part of the heat source. In particular, the invention overcomes the problem by surrounding the heat source where the hot target fluid is captive inside the pipes or containers, where there is continuous contact between the hot target fluid and the walls. In some cases, in standard systems, the walls of the pipes or container are not optimized for conducting heat. The invention modifies these walls to create conducting walls at the appropriate sections, in order to facilitate the heat recovery. For example, for p-traps, the walls could be made of metal (for example, copper, stainless steel, gold, silver, aluminium, bronze, brass, silicon carbide, beryllium oxide, tungsten, zinc) or other effective heat conductors (for example, graphite, graphene) at the area where the liquid is kept captive. For existing p-traps already installed, the modification is the addition of an outer structure containing the heat transfer fluid. In this instance, for example, the diameter of the outlet of the outer structure is smaller than the diameter of the inlet of the outer structure to control the flow of fluid. The outlet is either square, rectangular, or cylindrical; and/or can depend on the shape of the grease trap, the kitchen sink, or the shower p-trap. The smaller diameter of the outlet of the outer structure will increase the pressure and the velocity of the fluid. Another means of modifying the walls is to incorporate flow restriction elements therein, such as, for example, a baffle, a fin, a dimple plate, a plate (rectangular, oval, flat, or horizontal in form).

The heat recovery apparatus of the claimed invention is described in the appended claims. In one aspect, there is provided a heat recovery apparatus (1) comprising a housing (2) having an inlet (3) and an outlet (4), and an outer wall (5) and an inner wall (6) defining a central core (7), wherein the central core (7) accommodates a target fluid and wherein the inner wall (6) accommodates a heat recovery fluid.

In one aspect, the heat recovery apparatus (1) further comprises at least one static baffle (10) partially or wholly traversing the central core (7) and which is in fluid communication with the inner wall (6). Preferably, the at least one static baffle (10) is positioned at least 150mm from the inlet (3).

In one aspect, the at least one static baffle (10) is positioned at least 150mm and no more than about 300mm from the inlet (3).

In one aspect, the at least one static baffle (10) traverses the width of the central core (7).

In one aspect, the at least one static baffle (10) partially traverses the width of the central core (7) forming a primary baffle (10a) and a secondary baffle (10b), each of which is in fluid communication with the inner wall (6).

In one aspect, the target fluid and the heat recovery fluid flow in opposite direction to each other.

In one aspect, the temperature of the target fluid and the temperature of the heat recovery fluid differ by at least 5°C, and preferably no greater than 75°C. Preferably, the temperature of the target fluid and the temperature of the heat recovery fluid differ by between about 10°C and about 70°C or by between about 10% and 60%. Ideally, the temperature of the target fluid and the temperature of the heat recovery fluid differ by about 20°C.

In one aspect, the inner wall (6) is a thermally conductive wall. Preferably, the thermally conductive wall is composed of a material selected from the group comprising copper, aluminium, platinum, gold, silver, iron, steel, brass, bronze, graphite, graphene, concrete, or combinations thereof.

In one aspect, the outer wall (5) is a thermally insulating wall. Preferably, the thermally insulating wall is composed of a material selected from the group comprising mineral wool, cellulose, polyurethane, foam, polyurethane foam, polystyrene, fibreglass, or combinations thereof.

In one aspect, a pressure differential is applied between the inlet (3) and the outlet (4) to drive circulation of the heat recovery fluid.

In one aspect, the inner wall (6) further comprises at least one agitator to create turbulence of the heat recovery fluid. Preferably, the agitator is selected from an impellor and an internal baffle.

In one aspect, the target fluid is accommodated within a trap. Preferably, the trap is accommodated within the central core (7). In one aspect, In one aspect, the trap is selected from a substantially II, S, Q, or J-shaped pipe located below or within a plumbing fixture.

In one aspect, the heat recovery fluid is selected from a gas or mixture of gases, or a liquid or mixture of liquids.

In one aspect, there is provided a trap comprising the heat recovery apparatus (1) described herein.

In one aspect, there is provided a grease trap comprising the heat recovery apparatus (1) described herein, wherein the heat recovery apparatus (1) comprises a housing (2) having an inlet (3) and an outlet (4), an outer wall (5) and an inner wall (6) defining a central core (7), wherein the central core (7) accommodates a target fluid and wherein the inner wall (6) accommodates a heat recovery fluid; and at least one static baffle (10) partially or wholly traversing the central core (7) and which is in fluid communication with, and perpendicular to, the inner wall (6). In one aspect, the grease trap further comprises a first compartment (16) having at least one baffle selected from a static baffle (10), a primary baffle (10a), a second baffle (10b), or a combination thereof.

In one aspect, the grease trap further comprises a first compartment (16) having at least one baffle selected from the static baffle (10), a primary baffle (10a), a secondary baffle (10b), or a combination thereof.

In one aspect, the grease trap further comprises a target fluid entrance (12) and a target fluid exit (14), wherein the target fluid entrance (12) further comprises a fluid flow disruptor (20) attached thereto. In one aspect, the at least one static baffle (10) is positioned at least 150mm from the inlet (3). In one aspect, the at least one static baffle (10) is positioned at least 150mm and no more than about 300mm from the inlet (3).

In one aspect, the at least one static baffle (10) traverses the width of the central core (7). In one aspect, the at least one static baffle (10) partially traverses the width of the central core (7) forming a primary baffle (10a) and a secondary baffle (10b), each of which is in fluid communication with the inner wall (6).

In one aspect, the target fluid and the heat recovery fluid flow in opposite direction to each other.

In one aspect, the temperature of the target fluid and the temperature of the heat recovery fluid differ by at least 5°C, and no greater than 75°C. In one aspect, the temperature of the target fluid and the temperature of the heat recovery fluid differ by between about 10°C and about 70°C or by between about 10% and 60%. In one aspect, the temperature of the target fluid and the temperature of the heat recovery fluid differ by about 20°C.

In one aspect, the inner wall (6) is a thermally conductive wall. In one aspect, the thermally conductive wall is composed of a material selected from the group comprising copper, aluminium, platinum, gold, silver, iron, steel, brass, bronze, graphite, graphene, concrete, or combinations thereof.

In one aspect, the outer wall (5) is a thermally insulating wall. In one aspect, the thermally insulating wall is composed of a material selected from the group comprising mineral wool, cellulose, polyurethane, foam, polyurethane foam, polystyrene, fibreglass, or combinations thereof.

In one aspect, a pressure differential is applied between the inlet (3) and the outlet (4) to drive circulation of the heat recovery fluid.

In one aspect, the inner wall (6) further comprises at least one agitator to create turbulence of the heat recovery fluid. In one aspect, the agitator is selected from an impellor and an internal baffle (22,23). In one aspect, the target fluid is accommodated within the grease trap. In one aspect, the grease trap is accommodated within the central core (7). In one aspect, the heat recovery fluid is selected from a gas or mixture of gases, or a liquid or mixture of liquids.

The invention can be used to recover heat from standard p-traps in plumbing structures by surrounding the standard p-trap, providing an opportunity to recover heat from the captive fluid in the p-trap. In another instance, the invention replaces the p-trap section of the piping with a purpose-built p-trap integrated with the heat recovery unit.

The invention enables heat recovery from standard grease traps. The invention (totally or partially) surrounds standard grease traps, providing an opportunity to recover the heat typically lost to the environment.

In another instance, the invention replaces the grease trap with a purpose-built grease trap, integrated with the heat recovery unit. In this case, the modified grease trap may also contain a plurality of internal baffles for heat recovery inside the grease trap, in addition to the external heat recovery system.

In a further instance, the integrated grease trap and heat recovery apparatus have been modified to optimize several key parameters such as the internal fluid flow and the heat.

In one aspect, there is provided a heat recovery apparatus through the use of at least one internal baffle having an internal cavity that allows the heat recovery fluid to run therethrough, and the placement of the partition in an optimum place to increase the solid containing capacity of the grease trap and increase the time between maintenance interventions if they are required. The partition is typically positioned close to the outlet without impacting the operational efficiency of the grease trap and its purpose. Baffles are typically introduced to control/direct the flow within the grease trap. The baffle here is optimised for maximising heat transfer because the baffle introduces turbulence to the flow of the fluid. The baffle is typically positioned 150mm to 300mm away from the inlet (in the direction of the outlet, controlling the flow and adding some turbulence) and is the first baffle that will encounter the fluid as its hottest coming from source. In one aspect, the baffles can be hollow allowing the heat gaining liquid to flow, maximizing the contact surface area for heat transfer. The use of a separator, a typically vertical wall, holds the grease in the first cavity of the grease trap, effectively separating the grease from water, helping both to separate from each other.

Definitions

In the specification, the term “fluid” should be understood to mean a substance that continually deforms (flows) under an applied shear stress, or external force. Fluids are a phase of matter and include liquids, gases and plasmas. They are substances with zero shear modulus, or, in simpler terms, substances which cannot resist any shear force applied to them. Further examples of fluids include wastewater, oil, gas, liquified fats, gels, foams, sludge, and mixtures thereof.

In the specification, the term “target fluid” should be understood to mean the fluid of interest from which the heat or energy is being recovered, which is defined above.

In the specification, the term “recovery fluid” or “heat recovery fluid” should be understood to mean the fluid within the heat recovery apparatus of the invention which recovers the heat or energy from the target fluid. Examples of the heat recovery fluid include water, water-glycol solutions, steam, (natural or artificial) refrigerants, chilled water, heavy water, liquid metals (for example, gallium), and the like. In principle, any substance with fluid properties at the operating temperatures could be considered.

In the specification, the term “trap” should be understood to mean a section of piping where some fluid is retained after use. In plumbing, a trap is a device shaped with a bending pipe path to retain fluid to prevent sewer gases from entering buildings while allowing waste materials to pass through. In domestic applications, traps are typically II, S, Q, or J-shaped pipe located below or within a plumbing fixture. The p-trap is the most used configuration and resembles a substantially U-shaped pipe. In oil refineries, traps are used to prevent hydrocarbons and other dangerous gases and chemical fumes from escaping through drains. The recovery system of the claimed invention can be used in heat recovery applications around or within traps in homes, facilities, and industrial settings, including sewers, pipes, drains, and grease traps.

In the specification, the term “p-trap” should be understood to mean a substantially U- shaped trap having an inlet and an outlet connected by a substantially U-shaped pipe. In the specification, the term “grease trap” should be understood to mean a type of trap designed to intercept most greases and solids before they enter a wastewater disposal system. Common wastewater contains small amounts of oils which enter septic tanks and treatment facilities to form a floating scum layer. This scum layer is very slowly digested and broken down by microorganisms in the anaerobic digestion process. Large amounts of oil from food preparation in restaurants can overwhelm a septic tank or treatment facility, causing release of untreated sewage into the environment. High- viscosity fats and cooking grease such as lard solidify when cooled and can combine with other disposed solids to block drainpipes. Grease trap works by slowing down the flow of warm/hot greasy water and allowing it to cool. As the water cools, the grease and oil in the water separate out and float to the top of the trap. The cooler water - minus the grease - continues to flow down the pipe to the sewer.

In the specification, the term “baffle” or “static baffle” should be understood to mean a flow-directing or obstructing vane or panel used in tube heat exchangers, chemical reactors, and static mixers.

In the specification, the term “thermally conductive material” should be understood to mean a material that conducts heat.

In the specification, the term “solid containing capacity” should be understood to mean the amount of solid/food waste that can be stored in a grease trap before it must be cleaned - this tends to be roughly 25% of the overall operating capacity of a grease trap built under the specifications of EN 1825 (a European standard).

Brief Description of the Drawings

The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which: -

Figure 1A illustrates a heat recovery apparatus of the claimed invention, while Figure 1 B illustrates the heat recovery apparatus of Figure 1 A surrounding a heat source (a p-trap in this example).

Figure 2A illustrates an end elevation of a heat recovery apparatus according to the invention around a heat source (in this case, a grease trap), Figure 2B illustrates a plan view of the heat recovery apparatus of Figure 2A; and Figure 2C illustrates a cross section view of one aspect of the heat recovery apparatus of Figures 2A and 2B. Figure 3A illustrates a plan view of a heat recovery apparatus according to the invention around a heat source (in this case, a grease trap) and Figure 3B illustrates an end elevation view of the heat recovery apparatus of Figure 3A.

Detailed Description of the Drawings

The present invention provides a heat recovery apparatus for use in transferring the heat from a target fluid into a recovery fluid (through a thermally conducting wall), which is continuously running through the heat recovery apparatus of the claimed invention. For example, the heat recovery apparatus surrounds a p-trap structure to maximise the heat recovery from the target fluid. The recovered heat or energy is transported by the recovery fluid into a heat pump, a boiler, or similar device, to harvest the recovered heat.

Referring now to the figures, where Figure 1 illustrates a general embodiment of a heat recovery apparatus of the present invention that can be used in conjunction with a grease trap. Specifically, Figure 1 illustrates one aspect of the present invention, and is generally referred to by reference numeral 1. The apparatus 1 of the illustrated embodiment comprises a housing 2 having an inlet 3 and an outlet 4. The housing 2 further comprises an outer wall 5 and an inner wall 6. The inner wall 6 of the housing 2 defines a central core 7 within which a target fluid is accommodated. The inlet 3 and the outlet 4 are in fluid communication with the inner wall 6. The inner wall 6 is a conduit which accommodates a recovery fluid which recovers heat from the target fluid within the core 7. The recovery fluid enters inlet 3, flows through the inner wall 6 and exits through outlet 4 to a heat pump, a boiler, or similar device, to harvest the recovered heat.

In one aspect, the core 7 surrounds a waste pipe, such as a standard structure, which has a target fluid running down and accumulated in the substantially U-shaped section to prevent odour. When the target fluid is accumulated at the, the target fluid is typically above ambient temperature, and is continually being replaced by often warmer target fluid when the sink or other source of the target fluid is in operation. The recovery fluid flowing through the inner wall 6 is at a temperature that is below that of the target fluid. The inner wall 6 is typically formed from a thermally conductive material which enhances the recovery fluid’s ability to recover the heat from the target fluid in the core 7. Figure 1 B illustrates a heat recovery apparatus 1 of the Figure 1A surrounding the bottom part of a standard p-trap. For example, the target fluid is typically between 25°C and 60°C. The recovery fluid enters the system at between 8°C and 15°C, and the temperature of the recover fluid increases by at least 50%. The difference between the target fluid and the recovery fluid is a minimum of 10°C, but ideally a difference of more than 20°C. This is different from prior art heat recovery systems because the system of the claimed invention can recover high temperatures from areas where it is usually wasted, like grease traps and p-traps, recovering at least 50% of heat which is more than other heat recovery systems.

Figure 2A, 2B and 2C show a schematic illustration of a grease trap comprising the heat recovery apparatus of the claimed invention. In one aspect, the heat recovery apparatus 1 further comprises at least one static baffle 10 that traverses across the whole or part of the core 7 (see Figure 2B). The static baffle 10 reduces the flow of the target fluid but does not hinder the flow of the target fluid. The static baffle 10 does not create a separate, sealed compartment within the apparatus 1. In one aspect, when the at least one static baffle 10 traverses partway across the core 7 forming a primary baffle 10a and a secondary baffle 10b juxtaposed therefrom, the target fluid flowthrough the trap relatively unhindered in the direction of arrow B (see Figure 2C). The at least one static baffle 10 (and the primary baffle 10a and the secondary baffle 10b) is continuous with the inner wall 6. In use, the target fluid enters the trap through entrance 12, flows through the trap and out through the exit 14. The recovery fluid enters through the inlet 3 in the direction of arrow A that is in contra-flow to the direction of the target fluid. The recovery fluid flows through the inner wall 6, into the static baffle 10 (and the primary baffle 10a and the secondary baffle 10b), and out through the outlet 4 to a heat pump, a boiler, or similar device, to harvest the recovered heat. The at least one static baffle 10 is arranged in the first chamber 16 of the grease trap where the target fluid first enters the trap. The arrangement of the at least one static baffle 10 increases the flow path in the first chamber 16, thus slowing down the flow of the target fluid, and increases the separation time of the grease, sediment, and water.

Figures 3A and 3B show a schematic illustration of a heat recovery apparatus of the claimed invention around a grease trap. The heat recovery apparatus 1 comprises at least one static baffle 10 that traverses across the whole or part of the core 7 (see Figure 3B), in a similar fashion to that shown in Figure 2B/2C. In one aspect, when the at least one static baffle 10 traverses partway across the core 7 forming a primary baffle 10a and a secondary baffle 10b juxtaposed therefrom, the target fluid flow through the trap relatively unhindered from the entrance 12 through the trap and out through the exit 14 (see Figure 3B). The at least one static baffle 10 (and the primary baffle 10a and the secondary baffle 10b) is continuous with the inner wall 6. In use, the target fluid enters the grease trap through entrance 12, flows through the grease trap and out through the exit 14. The entrance 12, which acts as the target fluid inlet, further comprises a fluid flow disruptor 20 which acts to create more turbulence by making the target fluid hit the inner wall 6 first, therefore more heat can be recovered quicker.

The apparatus 1 also comprises baffles 22,23 that traverse the inner wall 6 where the target fluid will flow and exchange heat with the recovery fluid (see Figures 3A/3B).

The arrangement of the primary baffle 10a and the secondary baffle 10b slows down and controls the flow of the fluid coming into the first chamber 16, adding further turbulent flow of the fluid in the first chamber 16 and the core 7, while increasing the separation time of the grease, sediment, and water. When the fluid enters the first chamber 16 and meets the primary baffle 10a, the fluid flows downwards adding turbulence and increasing the time to separate, for example, grease and solids due to the difference in density. The secondary baffle 10b typically is in contact with the floor of the core 7, so that when the fluid hits the secondary baffle 10a, the flow of the fluid is disrupted giving it more time to separate. The primary and secondary baffles, 10a and 10b respectively, can also be hollow, allowing the recovery fluid to flow through the centre of the grease trap and absorb more heat from the target fluid.

The heat recovery apparatus 1 can also be integrated within traps.

The fluid within the heat recovery apparatus 1 is gaining heat all the time as the fluid is being pumped in a constant loop motion through the housing 2 that surrounds or is surrounded by warmer target fluid (for example, a grease trap or p trap wastewater). The fluid flowing within the apparatus 1 can be reused since the flow of fluid is in a loop. If the levels of the fluid begin to drop with the apparatus 1 , the level of the fluid can be supplemented with fresh fluid.

The technical advantage of the invention are provided in the following examples:

• Reduced heat loss, due to the capture of most of the heat which would otherwise be lost through the external surfaces of systems containing fluids.

• This is obtained through the increase of the heat exchange area at relevant locations, in particular where captive fluid is present (for example in p-traps and grease traps). • The invention is an external heat recovery apparatus which can be employed in addition to usual heat recovery devices of the internal recovery type.

• The invention can be added to existing standard structures: for example, p-traps and grease traps, pumping stations, holding tanks and eco chambers.

• The heat recovery apparatus can also be incorporated into p-traps or grease traps, etc. for heat recovery.

When integrated with traps, such as grease traps, the heat recovery apparatus of the claimed invention provides the following advantages: o Improved location of the separator in the grease trap, to enable higher sediment capacity at the same optimal 25% of height (max for efficiency of the grease trap). o Improved design of the baffles by placing them 150mm to 300mm away from the inlet (in the direction of the outlet, controlling the flow and adding some turbulence) and is the first baffle that will encounter the fluid at its hottest coming from source to optimize both grease trap and heat exchange, by increasing the flow path in the first chamber and increasing the separation time of the grease, sediment and water. This arrangement extracts maximum heat and direct flow and residue through a modified shape of the at least one baffle. The baffle’s shape can be modified by changing the orientation of the baffle with respect to the flow of the target fluid, changing the geometry of one or more baffles in the system (for example, changing from a triangular configuration to a chevron shaped configuration), the curvature or planarity of the baffle, the thickness of the walls one or more of the baffles, internal structure incorporating heat exchange, or a combination of these. The fluid can also flow through the baffles since they can be hollow, having more surface area to recover heat. Also, baffles can be integrated in the inner walls where the heat recovered from the fluid flows. o Increase in early heat transfer at the first re-engineered baffle. As most of the heat is transferred at the first baffle that the target fluid encounters, the first baffle is typically engineered as described above to maximise heat transfer, which reduces the opportunity for subsequent heat loss across the outer walls of the housing and opening as the target fluid proceeds through the trap.

• Re-design of the separator/partition structure for heat transfer purposes in the same manner as the baffles have been designed, as described above. By taking advantage of the holding tanks, the separator has been designed to also extract heat from the target fluid.

• Retrofittable: the heat recovery apparatus of the claimed invention can be designed to work with existing devices (p-traps and grease traps) or can be integrated into a new design optimizing performance of p-traps and grease traps both for their original intended function and for the purpose of heat recovery. For example, typically the wall of a grease trap where the fluid is captive is not optimised for heat conduction. The system described here permits the re-engineering of the grease trap in order to make that section of the wall heat conductive, thus extracting heat from the target fluid.

• Reduced maintenance: easy to clean.

• Improved longevity and environmental friendliness.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms “include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.