FORM 2
THE PATENTS ACT, 1970
(39 of l970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Apparatus for recovery of heat from a waste heat fluid
APPLICANTS
Larsen & Toubro Limited, Hydrocarbon IC, R & D Building, 3rd Floor, Gate 1, Powai Campus (W), Saki Vihar Road, Mumbai 400072, Maharashtra, India, an Indian Company
INVENTORS
Kaushik Arvind Satyapraskah and Chitta Nageswara Rao, both of Larsen & Toubro Limited, Hydrocarbon IC, R & D Building, 3rd Floor, Gate 1, Powai Campus (W), Saki Vihar Road, Mumbai 400072, Maharashtra, India, both Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an apparatus for recovery of heat from a waste heat fluid.
BACKGROUND OF THE INVENTION
Several industrial processes, such as steel making processes or cement manufacturing processes, consume vast quantities of energy and release considerable amounts of heat to the environment through waste gas, also known as off-gas or flue gas. Steel Making processes employ electric arc furnaces which often operate intermittently and hence the off-gas flow also can be intermittent. However, flow of hot off-gas from the furnaces can be very large with high heat recovery potential of the order of 50 MW for a typical 100 MT steel making electric arc furnace while cooling the hot gas from approximately 1200°C to 300°C. Off-gas from the furnace passes through a combustion chamber to burn any combustible components present therein. Subsequently, the gas flows through a water cooled duct where it is cooled to a temperature of around 600°C. Off-gas is further cooled in a forced draft air cooler to around 300°C before mixing with other cooler gases and letting out to the environment by passing through dust removal systems like bag filters and finally through the vent/ stack. Although hot flue gas is a very inexpensive hot fluid source, heat from the off-gas is generally let out to the environment and wasted.
WO 2010/18597A2 and corresponding US Publication 2010/0319348A1 describe a waste heat recovery system and a method of recovering waste heat, in particular waste heat of flue gas from electric arc furnace steel making processes using direct evacuation control. A first heat exchanger is configured to receive waste heat fluid from a waste heat fluid source and transfer the thermal energy from the waste heat fluid to a heat transfer fluid. A second heat exchanger is configured to transfer energy from the heat transfer fluid to a working fluid. A

power production system is configured to convert the transferred energy in the working fluid into electrical energy. The heat exchangers are provided with a hot heat transfer fluid storage tank and a cold heat transfer fluid storage tank to receive and if necessary store the hot and cold heat transfer fluids, respectively. The heat recovery system also comprises circulation pumps to pump the heat transfer fluids. The heat transfer fluid includes mixtures of molten nitrate salts and the working fluid includes water.
As the heat recovery system comprises a large number of equipments and devices, it is very expensive and it is very difficult to operate and maintain the system. The system is also bulky thereby occupying large area. Pumping and circulation of the heat transfer fluid through the storage tanks and power production system is also difficult to carry out. In order to control the temperature of the working fluid, heat tracing elements are required in the piping for the flow of the hot working fluid. This further increases the cost of the system. As the heat transfer fluid travels through multiple equipments and devices, there is also considerable loss of thermal energy. As a result, the heat recovery system and method are also not energy efficient. Further, in order to reduce energy losses, the system requires heavy insulation thereby further increasing the cost of the system. Still further, only forced convection mode of heat transfer between the heat transfer fluid and working fluid is possible in the above system.
In heat exchangers like tube and tube or tube and shell heat exchangers, two fluids namely a heat exchange fluid such as waste heat fluid and a working fluid and in multistream heat exchangers multiple fluids, namely multiple heat exchange fluid(s) and working fluid(s) flow through the heat exchangers simultaneously in order to effect heat transfer from the heat exchange fluid(s) to the working fluid(s) and to effect heat recovery by the working fluid(s).

Necessarily the two or all the fluids are to flow simultaneously. Heat transfer from the heat exchange fluid(s) to the working fluid(s) takes place directly and instantaneously. As the two or all the fluids are to simultaneously flow, heat exchangers by themselves can be used only for those applications where heat exchange or transfer can take place instantaneously. Therefore, it is not possible to use heat exchangers by themselves for applications where the hot heat exchange fluids with thermal energy received can be stored for sometime and then used as and when required to transfer the heat energy to the working fluid(s). Further in order to improve the heat transfer efficiency of the heat exchangers, it is necessary to precisely control the flow rates of the heat exchange fluid(s) and working fluid(s) therein. As a result, operation of the heat exchangers is quite difficult and cumbersome to carry out. Multistream heat exchangers are also complex and complicated in construction.
SUMMARY OF THE INVENTION
According to the invention there is provided an apparatus for recovery of waste heat from a waste heat fluid comprising an enclosed tank made of a mechanically strong material and thermally insulated at the outer surface thereof, the tank containing a heat storage and transfer medium capable of forming a convection current therein and comprising atleast one set of thermally conducting material waste heat fluid flow tubes extending horizontally through the heat storage and transfer medium at the bottom of the tank and connected to a common waste heat fluid inlet at the inlet ends thereof and to a common waste heat fluid outlet at the outlet ends thereof and atleast one set of thermally conducting material working fluid flow tubes extending horizontally through the heat storage and transfer medium at the top of the tank and connected to a common working fluid inlet at the inlet ends thereof and to a common working fluid outlet at the outlet ends thereof.

The heat storage and transfer medium is selected from meltable mixtures of nitrates salts such as sodium and potassium nitrate salts, thermic fluids such as Therminol™ of Solutia Inc, USA water or organic fluids such as ammonia. In case the heat storage and transfer medium is of the freezing type, the apparatus of the invention comprises heating means provided in the heat storage and transfer medium at the top of the tank to heat and melt the heat storage and transfer medium to the required temperature.
In case the apparatus of the invention is required to be operated at higher pressures above the atmospheric pressure, the apparatus of the invention comprises a cover gas blanket formed at the top of the tank above the heat storage and transfer medium in order to prevent vaporization of the heat storage and transfer medium at the higher pressures. The cover gas can be any gas which does not react with the heat storage and transfer medium and the tank. Preferably, the cover gas is selected from nitrogen, argon or helium. Steam can also act as the cover gas in case the heat storage and transfer medium is water/steam based. The apparatus of the invention including the cover gas blanket also comprises a cover gas inlet and a cover gas outlet at the top of the tank. Cover gas blanket may also be required if the heat storage and transfer medium operated at atmospheric pressures reacts adversely with the atmosphere so asto prevent ingress of the atmosphere.
The apparatus may comprise a forced convection inducing device for the heat transfer and storage medium. In case the heat storage and transfer medium and cover gas are reactive, the tank of the apparatus comprises a non-corrosive material lining at the inner surface thereof.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
In the accompanying schematic drawings;
Fig 1 is a crosssectional view of the apparatus for recovery of waste heat from a waste heat fluid according to an embodiment of the invention;
Fig 2 is a side view of the apparatus of Fig 1;
Figs 3, 4, 5 and 6 are crosssectional views of the apparatus for recovery of waste heat from a waste heat fluid according to different other embodiments of the invention; and
Figs 7 and 8 are crosssectional view and plan view of the apparatus for recovery of waste heat from a waste heat fluid according to another embodiment of the invention, respectively.
DETAILED DESCRIPTION OF THE INVENTION
The apparatus la for recovery of waste heat from a waste heat fluid such as flue gas from an electric arc steel making furnace, as illustrated in Figs 1 and 2 of the accompanying drawings comprises an enclosed tank 2a made of a mechanically strong material such as carbon steel or stainless steel. The tank is rectangular crosssection and is thermally insulated at the outer surface thereof with a thermally insulating material such as mineral wool marked 3. Besides, mineral wool, the tank outer surface can be also insulated with any other thermally insulating material. The tank contains a heat storage and transfer medium whose upper level is marked 4. The tank is also provided with a non-corrosive material lining 5 at the inner surface thereof. The non-corrosive material lining can be a refractory lining, for example, alumina

castable refractory. The non-corrosive lining is optional and is required only if the heat storage and transfer medium and the cover gas being referred hereafter is corrosive.
The tank comprises a set of thermally conducting material waste heat fluid flow tubes or pipes 6 extending horizontally through the heat storage and transfer medium at the bottom of the tank and connected to a common waste heat fluid flow inlet 7 at the inlet ends thereof and to a common waste heat fluid flow outlet 8 at the outlet ends thereof. The tank also comprises a set of thermally conducting material working fluid flow tubes or pipes 9 horizontally extending through the heat storage and transfer medium at the top of the tank and connected to a common working fluid inlet 10 at the inlet ends thereof and to a common working fluid outlet 11 at the outlet ends thereof. Both the set of tubes 6 and 9 are preferably circular, rectangular or square cross section and are preferably made of stainless steel or high alloy steel.
In order to recover heat from a waste heat fluid (not shown) in the apparatus of the invention, the heat storage and transfer medium in the tank is maintained in the liquid state and the waste heat fluid is allowed to flow through the waste heat fluid flow tubes 6 via the common waste heat fluid inlet 7. While passing through the waste heat fluid flow tubes 6, the waste heat fluid exchanges the heat energy thereof to the heat storage and transfer medium 4 in the tank 2a and exits the tank via the common waste heat fluid outlet 8. Due to the heat exchange, the heat storage and transfer medium at the bottom of the tank gets heated up and rises up in the tank continuously and the heat storage and transfer medium at the top of the tank at a lower temperature moves down continuously thereby establishing a natural convection current in the tank. As a result, the entire mass of the heat storage and transfer medium in the tank gets heated up uniformly. As the tank is thermally insulated at the outer surface

thereof, loss of heat to the ambient outside by way of conduction, radiation or convection is minimized and it is possible to store the heat in the heat storage and transfer medium for a considerably long period of time. It has been found that the heat can be stored in the tank for about a month or so.
Simultaneously or subsequently the heat from the heat storage and transfer medium within the tank is recovered by flowing a working fluid (not shown) through the working fluid flow tubes 9 at the top of the tank via the common working fluid inlet 10. The working fluid is, for example, water, air, or thermic fluid. While flowing through the working fluid flow tubes, the working fluid picks up the heat from the heat storage and transfer medium and gets heated up. The working fluid at a higher temperature exits the tank via the common working fluid outlet 11. The working fluid at a higher temperature is used for various applications like electric power generation, steam generation or preheating. The waste heat fluid exiting the tank may be taken through another apparatus of the invention to further recover heat from the waste heat fluid. Alternatively, if required, the waste heat fluid exiting the tank is further cooled and/or treated in known manner using known devices and/or equipments before being let out into the environment.
In case the heat storage and transfer medium is freezing type, a plurality of thermally conducting material hot fluid flow ducts 12 are provided at the top of the tank within the heat storage and transfer medium in order to heat up and melt the heat storage and transfer medium to the required temperature by passing a heating medium like a waste heat fluid or a fluid (not shown) heated up by a burner (not shown). When the heating medium flows through the hot fluid flow ducts, the heat storage and transfer medium gets heated up to the

required temperature and melts. The hot fluid flow ducts are preferably rectangular, circular or square cross section and are preferably made of stainless steel or high alloy steel.
In case the apparatus is required to be operated at higher pressures above the atmospheric pressure, a cover gas blanket 13 is formed at the top of the tank above the top level of the heat storage and transfer medium in order to prevent vapourisation of the heat storage and transfer medium at the higher pressures. The tank comprises a cover gas inlet 14 and a cover gas outlet 15 at the top thereof for the inflow and outflow of the cover gas.
The waste heat fluid flow tubes 6 and working fluid flow tubes 9 extend horizontally in the tank parallel to one another. However, the tubes 6 and 9 need not necessarily be parallel to one another. The flow of the waste heat fluid and working fluid in the respective tubes in the tank can be cocurrent or counter current.
The apparatus lb of Fig 3 of the accompanying drawings comprises a cuboidal tank with a rectangular crosssection and bottom of a segment of a circle marked 2b. The apparatus lc of Fig 4 of the accompanying drawings comprises an electric heater element 16 in order to heat and melt the heat storage and transfer medium to the required temperature and a cuboidal tank with a rectangular crosssection and bottom of a segment of a circle marked 2c. The apparatus Id of Fig 5 of the accompanying drawings comprises a cuboidal tank with a rectangular crosssection and bottom of a segment of a circle marked 2d and an electric heater element 16. The apparatus of Fig 5 also comprises an agitator 17 disposed in the tank. The impellers or blades of the agitator are marked 18. The shaft and drive motor of the agitator are marked 19 and 20 respectively. The motor is mounted on a bracket 21 which in turn is mounted at the top of the tank. While the waste heat fluid flows through the waste heat fluid

flow tubes 6, the agitator is operated to churn and turn the heat storage and transfer medium in the tank. As a result, heat exchange from the waste heat fluid to the heat storage and transfer medium and formation of the convection current within the heat storage and transfer medium are accelerated and the entire mass of the heat storage and transfer medium within the tank is uniformly heated up at faster rate.
The apparatus 1 e of Fig 6 of the accompanying drawings comprises a cuboidal tank with a rectangular crosssection and bottom of a segment of a circle marked 2e and hot fluid flow ducts 12. It also comprises a recirculation pump 22 connected to the tank for recirculation of the heat storage and transfer medium so as to agitate the heat storage and transfer medium and accelerate the heat exchange from the waste heat fluid flowing through the waste heat fluid flow tubes 6 to the heat storage and transfer medium and also to accelerate the convection current formation in the heat storage and transfer medium thereby heating up the entire mass of the heat storage and transfer medium in the tank at a faster rate uniformly.
The apparatus 1 f of Figs 7 and 8 of the accompanying drawings comprises a cuboidal tank with a rectangular crosssection and bottom of a segment of a circle marked 2f and hot fluid flow ducts 12. It further comprises a further set of waste heat fluid flow tubes 23 extending horizontally through the heat storage and transfer medium at the bottom of the tank parallel to one another and perpendicular to the waste heat fluid flow tubes 6. The waste heat fluid flow tubes 23 are connected to a common waste heat fluid inlet 24 at the inlet ends thereof and to a common waste heat fluid outlet 25 at the outlet ends thereof. The apparatus also comprises a further set of working fluid flow tubes 26 extending horizontally through the heat storage and transfer medium at the top of the tank parallel to one another and perpendicular to the working fluid flow tubes 9. The working fluid flow tubes 26 are connected to a common

working fluid inlet 27 at the inlet ends thereof and to a common working fluid outlet 28 at the outlet ends thereof. During operation of the apparatus, another waste heat fluid (not shown) from another waste heat fluid source is allowed to flow through the waste heat fluid flow tubes 23 and another working fluid (not shown) is allowed to flow through the working fluid flow tubes 26. In this apparatus, waste heat from two waste heat fluids are transferred to the heat storage and transfer medium and the heat from the heat storage and transfer medium is recovered using two working fluids.
The apparatus of the invention is compact and simple in construction and operation. All the functions of heat extraction, storage and transfer and recovery are carried out in the same apparatus. The heat storage and transfer medium makes it possible and affords the flexibility to recover and if necessary store heat from one or more waste heat fluids and to transfer the heat from the heat storage and transfer medium to one or more working fluid(s) or end use fluid(s) simultaneously or subsequently as and when required. The heat storage and transfer medium acts like a buffer heat for the working fluid(s) to interact with. The waste heat fluid(s) and working fluid(s) can be made to flow through the apparatus simultaneously or at different times. The apparatus can store the recovered thermal energy for a long period of time nearly about a month or so. The waste heat fluid(s) at a higher temperature will transfer the energy to the heat storage and transfer medium and the working fluid(s) at a lower temperature will absorb energy from the heat storage and transfer medium simultaneously or subsequently as and when required. The waste heat fluid(s) and working fluid(s) can flow in the apparatus independently of each other at different times or simultaneously while still achieving the required amount of heat transfer.

According to the invention it is also possible to carry out both natural and forced convection modes of heat extraction in the apparatus. The heat storage and transfer medium continues to remain in the apparatus and create natural or forced convection currents as required. There is no need for pumping or forcing the heat storage and transfer medium from one equipment to another equipment to achieve heat extraction, storage and transfer and recovery. Even when a recirculation pump is used to induce forced convection currents in the heat storage and transfer medium, only the heat storage and transfer medium is required to be recirculated and that too only in the tank. The invention eliminates the use of heat tracing elements. Being compact, cost of the apparatus including amount of insulation and insulation cost and space requirement for occupation of the apparatus are reduced. Maintenance cost of the apparatus is also reduced.
According to the invention, the apparatus can be operated in batchwise or continuous mode. If the waste heat fluid supply is intermittent, the apparatus can be advantageously operated in batch mode. The flow rates of the waste heat fluid(s) and working fluid(s) need not be critically controlled in both the instances of simultaneous heat recovery and subsequent heat recovery after a period of time as the efficiency of heat recovery will not be significantly affected by the flow rates of the waste heat fluid(s) and working fluid(s) in the apparatus.
In the case of certain heat storage and transfer medium such as meltable mixture of nitrate salts, the heating means (12 and 16) needs to be at the top of the salt mixture because during melting of the salt mixture the absorbed moisture in the salt mixture will be released as steam. If the heating means is at the bottom of the tank, the released steam can cause sputtering (splashing) of the salt mixture and this may create operational and safety

problems for the apparatus. Therefore, it is desirable to have the heating means at the top of the heat storage and transfer medium. However, the heating means can also be at the bottom of the tank in the case of other heat storage and transfer medium. Besides, the hot fluid flow ducts 12 and electric heater element 16, the heating means also can be of other construction and configuration. The tank geometry can be different. The tank can be cuboidal with a rectangular crossection and bottom of segment of an ellipse. The tank also can be cylindrical. A cylindrical tank can have a lower thickness as compared to a rectangular tank when operated at higher pressures as a cylindrical tank can withstand higher pressures with lower thickness as compared to a rectangular tank because of the absence of corners and stress concentration. Therefore, there can be cost benefit if a cylindrical tank is preferred at higher operational pressures.
Instead of having common waste heat fluid inlet(s) and common waste heat fluid outlet(s) and common working fluid inlet(s) and common working fluid outlet(s), the waste heat fluid(s) and working fluid(s) can flow directly into the respective tubes and exit directly from the respective tubes. There can be more than two sets of waste heat fluid flow tubes and working fluid flow tubes and more than two waste heat fluids and working fluids. Besides the agitator and recirculation pump, the forced convection inducing device can be of different construction and configuration. Such variations of the invention are obvious to a person skilled in the art and are to be construed and understood to be within the scope of the invention.
The following simulation example is illustrative of the invention but not limitative of the scope thereof.

Example 1
An enclosed stainless steel tank provided with mineral wool insulation externally was used for the simulation. The tank was cuboidal shaped with a rectangular crossection and bottom of segment of a circle. 900 waste heat fluid flow pipes of stainless steel having 73 mm outside diameter and 9.5 m length were considered at the bottom of the tank. 1000 working fluid flow pipes of stainless steel having 60.3 mm outside diameter and 9.5 m length were considered at the top of the tank.
470000 Kg Draw Salt (mixture of 46% NaN03 and 54% KN03) was provided in the tank. Initial Draw Salt temperature was 280°C. Waste heat fluid from an electric arc steel making furnace at 1200°C was simulated to flow through the waste heat fluid flow tubes at the flow rate of 30 kg/s. After the waste heat fluid flow was stopped, atmospheric air at 30 °C was simulated to flow through the working fluid flow tubes at the flow rate of 80 kg/s. The waste heat fluid flow was simulated for a time of 45 minutes followed by atmospheric air flow of 72 minutes.
The temperature of the waste heat fluid exiting the tank varied from 318 to 364 °C during the cycle time. The heat recovered by the Draw Salt reduced from 36.8 MW at the beginning to 35.1 MW at the end of the waste heat fluid flow. The outlet temperature of the air reduced from 319 °C at the beginning to 250 °C at the end of the air flow. The heat recovery by the air was 23.8 MW at the beginning and 18 MW towards the end. The temperature of the Draw Salt after a period of 96 hrs was still found to be 280 °C without any flow of waste heat fluid through the Draw Salt.

The above simulation clearly shows that there is significant amount of heat recovery from the waste heat fluid according to the invention and that the heat transferred to the Draw Salt can be stored and retained in the Draw Salt for a considerable period of time so as to facilitate recovery of the heat subsequently instead of being recovered simultaneously with the transfer of heat from the waste heat fluid to the Draw Salt.

We claim:
1. An apparatus for recovery of waste heat from a waste heat fluid comprising an enclosed tank made of a mechanically strong material and thermally insulated at the outer surface thereof, the tank containing a heat storage and transfer medium capable of forming a convection current therein and comprising atleast one set of thermally conducting material waste heat fluid flow tubes extending horizontally through the heat storage and transfer medium at the bottom of the tank and connected to a common waste heat fluid inlet at the inlet ends thereof and to a common waste heat fluid outlet at the outlet ends thereof and atleast one set of thermally conducting material working fluid flow tubes extending horizontally through the heat storage and transfer medium at the top of the tank and connected to a common working fluid inlet at the inlet ends thereof and to a common working fluid outlet at the outlet ends thereof.
2. The apparatus as claimed in claim 1, wherein the tank is thermally insulated at the outer surface thereof with mineral wool.
3. The apparatus as claimed in claim 1 or 2, wherein the tank comprises a non-corrosive material lining at the inner surface thereof.
4. The apparatus as claimed in claim 3, wherein the non-corrosive material lining comprises a refractory lining.
5. The apparatus as claimed in claim 4, wherein the refractory lining comprises alumina castable refractory.

6. The apparatus as claimed in anyone of claims 1 to 5, wherein the tank is made of carbon or stainless steel.
7. The apparatus as claimed in anyone of claims 1 to 6, wherein the waste heat fluid flow tubes and working fluid flow tubes are circular, rectangular or square crosssection.
8. The apparatus as claimed in anyone of claims 1 to 7, wherein the waste heat fluid flow tubes and working fluid flow tubes are made of stainless steel or high alloy steel.
9. The apparatus as claimed in any one of claim 1 to 8, wherein the heat storage and transfer medium comprises meltable mixtures of nitrate salts, thermic fluids, water or organic fluids.
10. The apparatus as claimed in any one of claims 1 to 9, wherein the tank comprises heating
means provided in the heat storage and transfer medium at the top of the tank.
11. The apparatus as claimed in claim 10, wherein the heating means comprises electric heater element.
12. The apparatus as claimed in claim 10, wherein the heating means comprises a plurality of thermally conducting material hot fluid flow ducts.
13. The apparatus as claimed in claim 12, wherein the hot fluid flow ducts are circular, rectangular or square crosssection.

14. The apparatus as claimed in claim 12 or 13, wherein the hot fluid flow ducts are made of stainless steel or high alloy steel.
15. The apparatus as claimed in anyone of claims 1 to 14, wherein the tank is rectangular crosssection or cuboidal with a rectangular crosssection and bottom of segment of a circle or an ellipse or cylindrical.
16. The apparatus as claimed in anyone of claims 1 to 15, wherein the tank comprises a cover gas inlet and a cover gas outlet at the top thereof and contains a cover gas blanket at the top thereof above the heat storage and transfer medium.
17. The apparatus as claimed in anyone of claims 1 to 16, which comprises a forced convection inducing device for the heat storage and transfer medium.
18. The apparatus as claimed in claim 17, wherein the forced convection inducing device comprises an agitator mounted in the tank.
19. The apparatus as claimed in claim 17, wherein the forced convection inducing device comprises a recirculation pump connected to the tank.
20. The apparatus as claimed in anyone of claims 1 to 19, wherein the waste heat fluid flow tubes and working fluid flow tubes in the tank extend parallel to one another.
21. The apparatus as claimed in anyone of claims 1 to 19, which comprises one set of waste heat fluid flow tubes extending horizontally through the heat storage and transfer

medium at the bottom of the tank and one set of working fluid flow tubes extending horizontally through the heat storage and transfer medium at the top of the tank.
22. The apparatus as claimed in claim 21, wherein the waste heat fluid flow tubes extend horizontally parallel to one another and the working fluid flow tubes extend horizontally parallel to one another.
23. The apparatus as claimed in anyone of claims 1 to 19, which comprises two sets of waste heat fluid flow tubes extending horizontally through the heat storage and transfer medium at the bottom of the tank and two sets of working fluid flow tubes extending horizontally through the heat storage and transfer medium at the top of the tank.
24. The apparatus as claimed in claim 23, wherein the waste heat fluid flow tubes of each of the two sets of waste heat fluid flow tubes extend horizontally parallel to one another and each of the two sets of waste heat fluid flow tubes is perpendicular to the other and wherein the working fluid flow tubes of each of the two sets of working fluid flow tubes extend horizontally parallel to one another and each of the two sets of working fluid flow tubes is perpendicular to the other.
25. The apparatus as claimed in anyone of claims 1 to 24, which is configured to allow waste heat fluid flow in the waste heat fluid flow tubes and working fluid flow in the working fluid flow tubes cocurrently or counter currently.