Field of the invention

The invention relates to heat recovery and utilization in general and more specifically a system for converting recovered thermal energy from an industrial plant to cooling of a cooling medium in a cooling infrastructure.

Related prior art

From prior art one should refer to general waste recovery technology wherein waste heat in an industrial plant in flue gas and/or from hot surface area is used to generate cooling, generate power, produce desalinated water and other similar purposes.

From prior art one should also refer to general waste recovery technology wherein waste heat in industrial processes such as aluminum electrolysis is recovered by heat exchangers and used for cooling generation, power generation, desalination and similar purposes.

At the same time such industrial processes, particularly electrochemical processes require large amounts of power and even with prior art the recovered power is low, complexities are high, and temperature of the recovery system is low and thus overall efficiency is low. This also brings in associated problems such as pollution.

Relevant technologies are MHD devices. ORC devices, absorption chillers and desalination devices. A MHD device can be a MHD generator mounted on a heat pipe. The heat pipe have a heat absorbing end for absorbing heat from a heat source. A part of the heat can be transformed to kinetic energy in a conducting working fluid because of phase change in the fluid when heatin. The heat pipe also have a heat extracting end for extracting electric energy, wherein at least one MHD generator is mounted onto the heat extracting end transforming a part of the kinetic energy in the working fluid into electric energy.

The organic Rankine cycle (ORC) uses an organic fluid such as n-pentane or toluene in place of water and steam. This allows use of lower-temperature heat sources, such as solar ponds, which typically operate at around 70-90 °C. The efficiency of the cycle is lower compared to an ordinary Rankine cycle as a result of the lower temperature range, but this can be worthwhile because of the lower cost involved in gathering heat at this lower temperature.

The traditional process used in desalination is vacuum distillation - essentially boiling it to leave impurities behind. In desalination, atmospheric pressure is reduced, thus lowering the required temperature needed. Liquids boil when the vapor pressure equals the ambient pressure and vapor pressure increases with temperature.

Effectively, liquids boil at a lower temperature, when the ambient atmospheric

pressure is less than usual atmospheric pressure. Thus, because of the reduced

pressure, low-temperature "waste" heat from electrical power generation or industrial processes can be employed.

In absorption chillers heat from a waste -heat source drives the process. The high affinity of the refrigerant for the absorbent (usually lithium bromide or ammonia) causes the refrigerant to boil at a lower temperature and pressure than it normally would and transfers heat from one place to another.

WO2012039624 and WO2013105867, both by another applicant, relate both to systems and methods for control of side layer formation in an aluminum electrolysis cell.

Objects of the invention

One object of the invention is an apparatus for converting thermal energy in an industrial plant from high temperature surface area.

Another object of the invention is an apparatus for converting thermal energy in an industrial plant from flue gas.

A number of non-exhaustive embodiments, variants or alternatives of the

invention are defined by the dependent claims.

A further object of the invention is an apparatus transferring the extracted thermal energy to a thermal energy utilization unit, more specifically to cooling of a cooling medium in a cooling infrastructure. An example of application is taking the waste heat of an aluminum plant and use it for cooling of a cooling medium transported in a system of isolated pipes in a geographical area

Summary of the invention The invention describes a system for recovery of waste heat from an industrial plant (100) comprising a heat source assembly. The heat source assembly comprises a flu-gas extraction unit concentrating flu-gas from the heat source, a flu-gas heat exchanger, a hot surface area exposing waste heat to its surroundings, a hot surface heat exchanger, a heat source circulating pump and a heating medium for transferring heat from the heat source,

Furter the system comprises a thermal energy conversion unit which in turn comprises a cooling medium heat exchanger, a heating medium heat exchanger, a thermal energy convertor which comprises one or more of the following convertor units: MHD device, steam/ORC device, absorption chiller and desalination device, and a converted energy distributor. The system furthermore comprises a cooling system comprising a pumping device and a cooling medium for transferring waste heat from the conversion unit.

Furthermore the heating and cooling medium is water and the energy convertor comprises one or more convertor units coupled in serial and in one of the following two orders: 1. MHD device, steam/ORC device, absorption chiller and desalination device and 2. MHD device, absorption chiller, ORC device and desalination device

Brief description of drawings

The above and further features of the invention are set forth with particularity in the appended claims and together with advantages thereof will become clearer from consideration of the following detailed description of an [exemplary] embodiment of the invention given with reference to the accompanying drawings.

The invention will be further described below in connection with exemplary embodiments which are schematically shown in the drawings, wherein:

Fig. 1 shows an embodiment with utilization of waste heat recovery in an industrial plant in a thermal energy conversion unit.

Fig. 2 shows an optimal order of convertor devices.

Detailed description

A system for recovering waste heat from an industrial plant 100 is provided and depicted in figure 1. The system comprises a heat source assembly 110, a thermal energy conversion unit 120 and a cooling unit 130. The heat source assembly 110 comprises a flu-gas extraction unit 111 with a flu gas heat exchanger 114 extracting heat from the flu-gas extraction unit 111. The heat source assembly 110 further comprises a hot surface area 112 with a hot surface heat exchanger 113 extracting heat from the hot surface area 112. The heat source assembly 110 also comprises a heat source circulating pump 115 that pumps a heat transport medium. Typically the heat source assembly is attached to an industrial an oven, a furnace or an aluminum electrolysis cell.

The mentioned heat transport medium will hereinafter be called the heating medium because it supplies heat from the heat source assembly 110 to the conversion unit 120 by means of a heating circuit. A medium that cools the conversion unit 120 is called the cooling medium and transports heat from the conversion unit 120 to the cooling unit 130 by means of a cooling circuit and thus cools the conversion unit 120.

The thermal energy conversion unit 120 comprises a cooling medium heat exchanger 121, a heating medium heat exchanger 122, a thermal energy convertor 123 and a converted heat distributor 124. The heating medium heat exchanger 122 receives the thermal energy from the heat source assembly 110, and the cooling medium heat exchanger 121 transfer thermal waste heat generated by the thermal energy convertor 123 to the cooling unit 130. In connection with the thermal energy conversion unit 120 a converted energy distributor 124 is attached. This cold for example be a network of pipes for heating or cooling, electric cables.

The thermal energy convertor 123 can comprise different convertor devices. A convertor device can be an electrical power generator such as a MHD device or an ORC device, a cooling generator such as an absorption chiller, a desalination device or other technology with similar functionality. The four mentioned units are explained in‘Related Prior Art’.

The cooling unit 130 comprises a cooling medium circulation pump 131 and a cooling tower. The cooling tower 132 may be substituted by other types of cooling equipment.

However the different convertor devices are working optimally in different temperature ranges: MHD device: 200 - 1000 C, steam/ORC device: 70-300 C, Absorption chiller: 100 - 200 and Desalination device: 50-100 C. It should be noted that we are now assuming that cooling is a desired effect near the plant. The devices should be ordered in serial such that each device is operating optimally. Not surprisingly the temperature ranges are overlapping, but from this list of temperature ranges we can deduce two possible optimal sequences of convertor devices: 1. MHD device, steam/ORC device, absorption chiller and finally desalination device and 2. MHD device, absorption chiller, ORC device and desalination device. With these two sequences of convertor devices more energy is converted than is possible by any one convertor device however optimized.

In one embodiment also the flu-gas heat exchanger 114 and the hot surface heat exchanger 113 are connected in parallel. The circulating medium is further transported through the heating medium circuit to the thermal energy conversion unit 120.

In one embodiment the cooling medium and the heating medium is water. This has the advantage of low costs and high degree of safety. The hot surface heat exchanger 113 could also use a heat pipe in the case where the convertor device 123 is a MHD device.

In a further embodiment the flu-gas extraction unit 111 unit and the hot surface area 112 further comprises a heat collection manifold wherein the flu-gas extraction unit 111 and the hot surface area 112 are connected in serial to the heat collection manifold further connected to the energy conversion unit 120.

In a further embodiment the flu-gas extraction 111 unit and the hot surface area 112 further comprising a heat collection manifold wherein the flu-gas extraction and the hot surface area are connected in parallel to the heat collection manifold further connected to the energy conversion unit 120.

In a further embodiment an array of energy conversion units (120) are cooled by one individual cooling system (130) or by an array of multiple cooling systems connected for example in a main ring arrangement.

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