FIELD OF THE INVENTION:

The present disclosure relates to a field of thermal energy conversion into mechanical energy. Particularly, the disclosure relates to an efficient system for 5 recovery of energy from low-temperature heat source. More particularly, the disclosure relates to a modified Kalina cycle for conversion of low temperature heat or thermal energy from low temperature heat sources into mechanical energy. The present disclosure also relates to process for converting a thermal energy from low temperature heat sources into mechanical energy. 10
BACKGROUND OF THE INVENTION:
Low-temperature energy source generally refers to a temperature below 200°C. Many low temperature waste heat streams are generated in the steel, cement, petrochemical, refinery and other industries. The low temperature waste heat streams include hot water, low-temperature flue gas and steam, process streams 15 that are cooled by dissipating heat to atmosphere in air/water cooler. These streams basically cannot be re-used in the production process to recover heat i.e. the energy from these streams cannot be reused in the process. The main reason is that the temperature of these streams is lower than the streams used in the process or heat surface area requirement would be large for process to process heat 20 exchange. These low temperature, low grade heat are abundant in the industry and find no application in the industry.
Further, the low-temperature energy streams cause damages to the environment when they are let out. Hence, on one hand the industry requires energy and on the other hand the low temperature heat is wasted by letting into the atmosphere. 25
Energy recovery and utilization from the low temperature energy streams not only reduces the energy consumption, but also reduces environmental pollution
3
and achieves energy saving effect. Thermodynamic cycles are usually used to recover the energy from the heat source.
The thermodynamic cycle is a continuous cycle which transfers energy, by heat exchange, from a hot source to a working fluid in the cycle. The working fluid, in pressurised vapor form, is then send to the turbine to generate the power. The 5 low-pressure vapor from the turbine is then send to exchange heat with low temperature cold source. Further, the working fluid passes through a pump, which pressurises it and coverts it into a liquid and vapour mixture. The working fluid is then passed through a throttle to convert the vapor in liquid completely. The high-pressure liquid is then passed to the heat exchange with hot source to 10 complete the cycle.
In a conventional Rankine Cycle (thermodynamic cycle), the recovery of heat from heat sources is used to make steam and further, the steam is then used to drive steam turbine to convert the thermal energy to mechanical energy. The turbine shaft power output is then used to generate electricity. Similarly, it is 15 possible to generate low pressure steam from low temperature heat to drive a low-pressure turbine and thus capture more useful work from the steam. However, such low-pressure turbines are relatively large and expensive. In addition, turbine blades in the low-pressure turbine erode at unacceptable rates, unless expensive reheat equipment is added. 20
Reference is made of US patent application 05/571212 which relates to a Waste heat recovery system where Waste heat in the form of the sensible heat of flue gases, sensible and latent heat of geothermal sources, etc., is converted to usable energy. When the energy source consists solely of sensible heat of a gas or a liquid which is not the working fluid, the liquid working fluid is heated by the 25 energy source and then expanded in a hot liquid turbine wherein partial vaporization occurs with decrease in pressure. Water is a preferred working fluid within the temperature range of 66oC to 260oC and may be used from ambient to its critical temperature. A working fluid of lower volatility is preferred for stages
4
at higher temperature and a more volatile working fluid for the stages at lower temperature. Though various cycles are already available, the one discussed in the present patent is regarding Kalina cycle.
Further, in the US patent 5,029,444, Kalina discusses about Simple Kalina Cycle. 5 The Kalina cycle is a thermodynamic cycle having solution of two fluids with different boiling points for its working fluid. Since the solution boils over a range of temperatures, more of the heat can be extracted from the source than with a pure working fluid. This provides efficiency comparable to a Combined cycle, with less complexity. The same applies on the exhaust (condensing) end. This 10 provides efficiency comparable to a Combined cycle, with less complexity
By appropriate choice of the ratio between the components of the solution, the boiling point of the working solution can be adjusted to suit the heat input temperature. Water and ammonia is the most widely used combination, but other combinations are feasible. Amount of Energy recovered by Ammonia‐Water 15 solution is higher as compared to pure water due to varying Boiling range .Kalina Cycle is favorable to other Organic Rankine Cycles (ORC) due to the advantage of multicomponent.
The advantages of Kalina cycle is as below:
• Any single component working fluid, due to pinch, approach point 20 limitations and a constant boiling point, cannot cool the gases to low temperature.
• Boiling of working fluid occurs over a range of temperatures.
• By virtue of varying boiling point, two component working fluid is able to "match" or run parallel to the heat source cooling temperature line while 25 recovering energy, hence the final exit temperature can be low.
• The condensation of two component working fluid also occurs over a range of temperatures and hence permits additional heat recovery in the condensation system.
5
• The condenser pressure can be much higher in two component fluid cycle, and the cooling water temperatures do not impact the power output
• Thermo-physical properties of mixture can also be altered by changing the concentration of one component
• Modifications to the condensing system are also possible by varying the 5 mixture concentration and thus more energy can be recovered from the low temperature heat source.
• Expansion in turbine can give a saturated vapor in two component fluid cycle compared to wet steam.
• Conventional equipment such as steam turbines can be used in two 10 component fluid cycle because of close molecular weight advantages
Although, the simple Kalina cycle provides efficiency comparable to a combined cycle, with less complexity, there exists a necessity of improve the efficiency of the Kalina cycle to extract more heat from the low temperature energy source or generate more mechanical energy /electrical power from the extracted heat 15 source.
Various modifications are carried out on Kalina cycle to optimise the cycle with various changes in heat absorption, flashing at various pressure, application of various heat sources, combining Kalina cycle with ORC, other cycles, choice of working fluids etc. 20
Reference is made to patent (US 0096862) wherein the inventor discusses about power generation utilizing flue gas streams and a multi-component working fluid, having a heat recovery vapor generator (HRVG) Subsystem, a multi-stage energy conversion or turbine Subsystem and a condensation thermal compression Sub system (CTCSS), where the CTCSS receives a single stream from the turbine 25 subsystem
6
Reference is made to CN102434235A and CN203948139U disclosing a Kalina cycle generation system adopting an ejector. The Kalina cycle of the document is a modified Kalina cycle with the ejector placed before the condenser. The ejector reduces the load on the condenser. Further, the ejector reduces the throttling loss of the original Kalina cycle power generation system which results in 5 improvement of the power generation efficiency and power generation capacity of the Kalina cycle.
Reference is made to US20170058719A1, which discloses a system for conversion of gas processing plant waste heat into power. The system is a Kalina cycle energy conversion system. The system disclosed is a complex system of 10 Kalina cycle involving a first and second groups of energy conversion heat exchangers, separators, first and second turbines. The complex Kalina cycle has ejector placed before the condenser.
Thus, there is a need to improve the efficiency of recovery of useful work obtainable from low temperature heat sources. In the case where the recovery 15 system is used to generate electricity, an advantage of improving efficiency is the lowering of operating costs per kilowatt-hour of energy produced. A further advantage is that the additional electrical energy obtained reduces the quantity of fossil fuel that would otherwise have been burned to produce a similar amount of electrical energy. Thus, there is less fossil fuel depletion, less air pollutant 20 production and less global warming due to carbon dioxide production.
Although the prior arts disclose various thermodynamic cycles to recover heat from low temperature streams, the systems or cycles know are either very complex or has low energy conversion efficiency. There is a need for a method and apparatus for increasing the efficiency of the conversion of such low 25 temperature heat to electric power that is not economically possible by efficiency of standard Rankine cycles that operates with water as working fluid or an Organic Rankine Cycles (ORC) which replace water with organic fluids having lower boiling point and also the Kalina Cycle with/ without an ejector.
7
So, there is a requirement for a system or thermodynamic cycle which produces more work/ improved energy conversion efficiency. The present invention provides such a method and apparatus.
In view of the above-discussion, the inventor of the present disclosure felt a need to develop a system which overcomes all the problems of the prior arts. 5 Particularly there is a need to improve the efficiency of the modified Kalina cycle. The present invention is simple i.e. it does not have any complex equipment in the cycles and has improved energy conversion efficiency.
SUMMARY OF THE INVENTION:
The present disclosure relates to a system and process for recovery of energy 10 from a low temperature energy source. Particularly, the disclosure relates to a thermodynamic cycle that converts the thermal energy from the heat source to the mechanical energy. The thermodynamic cycle takes heat energy from the heat source and converts part of it into the work (mechanical energy) and disposes the rest of the energy to the cold source. The disclosure relates to a modified Kalina 15 cycle (thermodynamic cycle) for efficiently converting the heat energy to mechanical energy. The Kalina cycle has more than one working fluid and so the energy recovery efficiency is more. The Kalina cycle of the present disclosure is modified to include the jacketed pressure recovery device as one of the components. The jacketed pressure recovery device in the Kalina cycle enhances 20 the efficiency of the energy recovery. The jacketed pressure recovery component is placed before the condenser. The stream of liquid from the bottom of gas liquid separator and the stream of gas/Liquid mixture or mainly gas with small portion of liquid from the turbine is feed to the jacketed pressure recovery device. The jacketed pressure recovery device reduces the load on the condenser and 25 improves the energy efficiency.
In further aspect of the present disclosure, a process for efficient energy recovery is disclosed. The process involves transferring heat from the low temperature heat
8
source to the process fluid in the Kalina cycle, converting the heat into work through Kalina cycle.
BRIEF DESCRIPTION OF FIGURES
The above and other aspects and advantages of the present invention will become apparent from the following detailed description embodiments, taken in 5 conjunction with drawings, wherein
Figure 1 is the process flow diagram of low level heat recover by modified Kalina cycle with pressure recovery device.
Figure 2 is schematic representation of the jacketed pressure recovery device.
Figure 3 is the process flow diagram of low level heat recover by modified 10 Kalina cycle with jacketed pressure recovery device.
DETAILED DESCRIPTION OF INVENTION
While the disclosure is susceptible to various modifications and alternative forms, specific aspects thereof have been shown by way of examples and will be described in detail below. It should be understood, however that it is not intended 15 to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternative falling within the spirit and the scope of the invention. The Applicants would like to mention that the examples and comparative studies are mentioned to show only those specific details that are pertinent to understanding the aspects of the present 20 disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.
The present disclosure relates to a system for recovery of energy from a low temperature energy source. Particularly, the disclosure relates to a 25 thermodynamic cycle that converts the thermal energy from the heat source to the mechanical energy. The thermodynamic cycle takes heat energy from the heat
9
source and converts part of it into the work (mechanical energy) and disposes the rest of the energy to the cold source. The disclosure relates to a modified Kalina cycle (thermodynamic cycle) for efficiently converting the heat energy to mechanical energy. The Kalina cycle has more than one working fluid and so the energy recovery efficiency is more. The Kalina cycle of the present disclosure is 5 modified to include the jacketed pressure recovery device as one of the components. The jacketed pressure recovery device in the Kalina cycle enhances the efficiency of the energy recovery. The jacketed pressure recovery component is placed before the condenser. The stream of liquid from the bottom of gas liquid separator and the stream of gas/Liquid mixture or mainly gas with small portion 10 of liquid from the turbine is feed to the jacketed pressure recovery device. The jacketed pressure recovery device reduces the load on the condenser and improves the energy efficiency.
In a further aspect of the present disclosure, a process for efficient energy recovery is disclosed. The process involves transferring heat from the low 15 temperature heat source to the process fluid in the Kalina cycle, converting the heat into work through Kalina cycle.
The invention provides a better system for efficient energy recovery from the low temperature energy source. This is achieved by using a jacketed pressure recovery device in the thermodynamic cycle. The jacketed pressure recovery 20 device has means for transferring the pressure energy to low pressure gaseous working fluid thus possibility of better absorption, condensation, low power consumption in pump.
In one particulate embodiment, the disclosure relates to a system for efficient energy recovery from low temperature heat source comprising a pump to convert 25 a low pressure multi-component working fluid stream into pressurised working fluid;
10
a heat exchanger (101) which partially or completely vaporizes the working fluid to produce high pressure stream (11) by transferring heat from the heat source, which is at a temperature of below 250oC;
a gas/liquid separator (102) which separates a high pressure vapor (12) and a high pressure liquid (18) from the high pressure stream (11); 5
an expander (104) which converts the heat energy from the high pressure vapor (12) to work energy;
a pressure recovery device (110), which increases the pressure of the high pressure liquid (18) and low pressure vapor (15) to produce a mixture stream (21) having a mixture of vapor and liquid phases, 10
characterized in that the pressure recovery device (110) has a converting (A) and diverging (B) section and the either or both of the sections has a jacketed cooling around the periphery, to reduce the temperature and produce the mixture stream (21);
a condenser (107) which converts the vapor phase into liquid phase in the mixture 15 stream (21) by transferring heat to the cold source (16).
In another embodiment of the system, the jacketed pressure recovery device has single inlet or multiple inlet and corresponding outlet for cooling water.
In yet another embodiment of the system, the jacketed pressure recovery device has fins on the ejector side for better heat recovery. 20
In yet another embodiment of the system, the temperature of the heat source in in the range of 50oC to 250oC.
In yet another embodiment of the system, the high pressure vapor (102) from the 25 separator (12) is passed through a super heater (103) to increase the temperature of the high pressure vapor (12).
In yet another embodiment of the system, the expander (104) of the system is a turbine and the work from the expander is converted into electrical energy by 30 electricity generator.
11
In yet another embodiment of the system, the pressurised working fluid from the pump (108) is passed through the recuperator (109) to transfer heat from the high pressure liquid (18) to the said pressurised working fluid.
5
In yet another embodiment of the system. the jacketed pressure recovery device (110) is cooled by the cold source.
In yet another embodiment of the system, the cold source is the cooling water.
10
In yet another embodiment of the system, the heat source is a flue gas from gas turbine exhaust, fired equipment like Boilers, furnaces, HRSg process stream or a low-grade heat being wasted to the atmosphere.
In yet another embodiment of the system, the working fluid is binary mixture 15 having fluid 1 and fluid 2.
In yet another embodiment of the system, the fluid 1 is selected from ammonia, propylene, propane and methanol; the fluid 2 is selected from water, butane, iso butane, pentane, iso-pentane and ethanol. 20
In another embodiment, the disclosure relates to a process for efficient energy recovery from low temperature heat source comprising steps of
pressurising a multi-component low pressure working fluid in a pump (108) to produce pressurised working fluid; 25
vaporising or exchanging heat from a heat source, which is below 250 oC, to the pressurised working fluid in a heat exchanger (101) to produce a high pressure saturated stream (11);
separating the gas and liquid phase of the high pressure saturated stream (11) in a gas/liquid separator (102) to produce high pressure vapor (12) and high pressure 30 liquid (18);
12
converting the heat energy from the high pressure vapor (12) to work in a expander (104) to produce a low pressure saturated vapor (15);
recovering pressure of the low pressure saturated vapor (15) and high pressure liquid (18) in a pressure recovery device (110) to produce the mixture stream (21), 5
characterized in that the pressure recovery device (110) has a jacketed cooling system around the periphery to reduce the temperature and produce the mixture stream (21),
condensing the vapor from the mixture stream (21) to produce the multicomponent low pressure liquid working fluid. 10
In another embodiment of the disclosure, the working fluid of the process is binary mixture having fluid 1 and fluid 2.
In another embodiment of the disclosure, the fluid 1 of the process is selected 15 from ammonia, propylene, propane and methanol and the fluid 2 of the process is selected from water, butane, iso butane, pentane, iso-pentane and ethanol.
The system and process of the present disclosure is designed to operate with a multi-component working fluid including at least two components of one lower 20 boiling component and a higher boiling component. The working fluid preferably is a multi-component fluid that comprises a lower boiling point component fluid and a higher boiling point component. In certain embodiments, the working fluids include an ammonia-water mixture, a mixture of two or more hydrocarbons, a mixture of two or more class of refrigerants, a mixture of hydrocarbons and class 25 of refrigerants, or the like. In general, the fluid can comprise mixtures of any number of compounds with favourable thermodynamic characteristics and solubility and Boiling point differences. The working fluid is a mixture of water and ammonia. The working fluid of the modified Kalina cycle exchanges heat from the low temperature heat source (10). 30
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The heat source stream is open circuit comprises a first pipe for introducing high temperature heat source stream into the superheater heat exchanger; a second pipe connecting the superheater heat exchanger to the vaporiser, for transmitting high temperature heat source stream there through.
Figure 1 discloses the modified Kalina cycle with ejector of the prior arts 5 disclosed in the back ground. The Kalina cycle has a ejector or pressure recover device (106).
Figure 2 discloses the jacketed pressure recovery device PRD (110) of the present disclosure. The jacketed pressure recovery (110) device has a converging section (A) and a diverging section (B). The pressure recovery device PRD increases the 10 pressure of the liquid (18) and gas (15) streams entering the PRD. The converging (a) and the diverging (B) section of the PRD increases the pressure of the streams by the throttling process. The mixture (21) coming out of the PRD is a increased pressure stream having mostly liquid. This is because that the increase in pressure leads to the conversion of the vapor into liquid phase. 15
The diverging section (B) of PRD is a jacketed one. The cooling liquid (19) passes through the jacket of the PRD. The diverging section (B) not only increases the pressure of the streams but also cools the streams. The PRD device of the present disclosure has the advantage of both reducing the pressure and cooling the streams. This leads to reduction in load of the condenser (107). 20
Figure 3 discloses the modified Kalina cycle having of the present disclosure having jacketed pressure recovery device. The Kalina cycle of the present disclosure has multi-component working fluid.
The modified Kalina cycle of the present disclosure is different from the Kalina cycle (Figure 1) of prior art such that the modification of the jacketed pressure 25 recovery device.
The working fluid exchanges heat with the low temperature heat source (10) which is in the temperature range of below 250oC. The heat source has a
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temperature of higher than 50oC. The heat exchanger or evaporator (101) is used to transfer heat from the low temperature heat source to the working fluid and vaporize it. The high pressure saturated stream (11) is produced from the evaporator (101). The saturated stream (11) is the combination of both vapor and liquid phase. The high pressure saturated steam (11) is passed through the 5 separator (102), which separates the vapor (12) and the liquid (18) streams. The high pressure gas steam (12) comes from the top of the separator and the high pressure liquid (18) comes from the bottom of the separator (102).
The high pressure saturated vapor (12) is passed though the heat source / super heater (103) to convert the high pressure saturated vapor as super-heated vapor 10 (14). The super-heated vapor (14) is passed through the expander or turbo generator (104) to extract the energy or convert the heat energy into work.
The high pressure saturated liquid (18) from the separator and the low pressure saturated vapor (15) from the expander is sent to the jacketed pressure recovery device (110) to increase the pressure and reduce the temperature of the stream. 15 The jacketed pressure recovery device (110) produces a mixture (21) mostly of liquid. The mixture is passed through the condenser (107) to condense the vapor form the mixture. The liquid steam from the condenser is pumped to increase its pressure before sending it to the heat source, thus completing the cycle.
The expander (104) is selected from the turbines and rotary expanders. Suitable 20 heat transfer fluids for use in this invention include, without limitation, melt able salts, synthetic heat transfer fluids such as THERMINOLR) (a registered trade mark of Solutia Inc. Corporation) and DOWTHERMR) (a registered trademark of Dow Chemicals Corporation), natural heat transfer fluids, other fluids capable of acting as a heat transfer fluid, and mixtures or combinations 25 thereof.
The closed circuit heat recovery apparatus of the present disclosure comprises an evaporator, a separator, a superheater, a expander, Recuperator, jacketed pressure recovery device, a condenser and a pump, wherein
15
a) The separator (102) is connected to the heat exchanger in which the working fluid vaporize and the vapor and liquid working fluid mixture as formed, wherein the vapor is separated from the liquid, said separator being in fluid communication with said evaporator and the superheater;
b) The superheater (103) has a heat exchanger for superheating gaseous 5 working fluid by transferring heat from low temperature hot streams, said super heater being in fluid communication with said separator and said expander;
c) The expander (104) has means for expanding the superheated gaseous working fluid to form low pressure gaseous working fluid, said expander being able to produce shaft work and being connected to a second machine for using 10 such work, said expander being in fluid communication with said superheater and said Jacketed pressure recovery device;
d) The jacketed pressure recovery device (110) has means for transferring the pressure energy to low pressure gaseous working fluid said jacketed pressure recovery device being in fluid communication with expander and condenser. This 15 jacketed pressure recovery device helps in reducing the size and load of the condenser by utilizing the pressure energy in the liquid from the Recuperator. The high pressure in the liquid is transferred to the gas and it thus assists in condensation process and immediately removing the heat formed through the cooling water of the jacketed pressure recovery device helps in faster heat 20 dissipation, faster condensation and thus less equipment size. Also, this helps in increase in pressure at the inlet of condenser thus helping to minimise pumping load or reducing the Turbine exhaust for producing more mechanical energy/ work/electrical energy. Also, this results in increasing the energy recovery and increased efficiency of the system 25
e) The condenser (107) has a heat exchanger for generating liquid working fluid by transferring heat from the working fluid to a cooling fluid to condense the working fluid, said condenser being in fluid communication with said jacketed pressure recovery device and said pump, and
16
e) The pump (108) is for raising the pressure and for pumping the liquid from the condenser to Recuperator exchanger; said pump being in fluid communication with said condenser and said Recuperator
f) The evaporator has a heat exchanger for evaporating liquid working fluid by transferring heat from low temperature hot streams, said evaporator being in 5 fluid communication with said separator and said Recuperator;
g) The Recuperator (109) has a heat exchanger by transferring heat from liquid coming from separator, said Recuperator being in fluid communication with said evaporator and pump;
The Water cooled Jacketed pressure Recovery device (instead of a simple ejector) 10 provides the advantage for the present invention. The reaction of Ammonia and water is exothermic in nature and based on the composition of mixtures, the temperature may raise by 10-30oC upon mixing of the liquid ex- Recuperator with that of the exhaust of the turbine. Generally, a condenser downstream after mixing of these streams recovers the heat. But is proposed to utilise a water 15 cooled jacketed pressure increasing device. Even having fins for better heat transfer. This helps in immediately disposing of the heat recovered by phase change of Ammonia + Water and other sensible heat generated. Thus, it helps in reducing/ completely replacing the downstream cooling water condenser.
In regions with water temperature very low / having low cost chilled water 20 availability, the size of the PRD shall also be reduced due to faster heat dissipation. In Cold countries, having air cooled over the water cooled can again will help further.
The modified Kalina cycle of the present disclosure also includes a splitting valve and a mixing valve. Splitting are used for stream splitting. These valves can be 25 manually adjustable or dynamically adjustable so that the splitting achieve the desired improved efficiency. The same is true for combining or mixing streams using mixing valves. This also can be manually adjustable or dynamically
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adjustable so that the mixing achieves a desired result such as full absorption of one stream into another stream.
Although the description mentions all the devices/equipments being involved in the modified Kalina cycle any modification of the flow by bypassing the equipment is also within the scope of the invention. The splitting valve and the 5 mixing valve can also be placed in the cycle to partially pass the stream through the equipment.
Example:
Example 1: In example 1, Ammonia-Water is considered as the working fluid in the thermodynamic cycle. The modified Kalina cycle according to the present 10 disclosure have been studied by varying the concentration of ammonia from 10 % - 95 % to take the advantage of multiple fluids of different boiling points. Predominantly, the % of Ammonia is maintained in the region of 60-75 %. The thermal efficiency of the system depends on the inlet and outlet temperature requirements of the heat source available and the system can be optimised 15 accordingly.
The operating conditions of the Kalina cycle such as flow rate, pressure and temperature are listed in the tables below. The Heat source available at 170oC is Flue gas from Gas Turbine exhaust and the heat source cannot be cooled below 110oC. Various cases can be considered based on the heat source available. 20
Various parameters like limitation of cooling water temperature, pressure at inlet of pump to maintain working fluid in liquid state, turbine exhaust temperature to maintain the dryness factor of the exhaust, pressure to be maintained in the system plays a key role and some are listed in the following tables.
Table 1-4 indicates the parameters related to different Ammonia concentrations 25 in the range of 60-75 (wt %). Three cases are studied by differing the flow rates.
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Table-1 Parameters related to Ammonia concentration of 60 (wt. %)
Parameters
Units
Case-1
Case-2
Case-3
Total Flow
TPH
200
150
100
Ammonia
wt%
60
60
60
Water
wt%
40
40
40
Pump Inlet Pressure
Kg/cm2g
6.4
6.4
6.4
Pump Discharge Pressure
Kg/cm2g
42.4
42.4
42.4
Recuperator Out Temp (Hot stream)
oC
55
55
55
Seperator-1 Inlet
Pressure
Kg/cm2g
40
40
40
Temp
oC
144
156
169
Vapor Fraction
0.36
0.45
0.54
Vapor
Ammonia
Wt.%
93.8
90.3
85
Water
Wt.%
6.2
9.7
15
Power gen
MW
3.90
3.77
3.17
Heat Duty
MW
30
30
25
Pump Duty
MW
0.330
0.249
0.166
Super Heat
MW
0
0
0
Turbine Out
oC
76.3
89.4
101.9
Vapor %
%
95
95
95
Net Power (Standalone)
MW
3.57
3.52
3.00
Thermal Eff. (Standalone)
%
11.78
11.64
11.92
19
Energy Saved Due to PRD
MW
0.19
0.12
0.07
Net Power (Including PRD)
MW
3.76
3.64
3.07
Thermal Eff. (Including PRD)
%
12.40
12.04
12.19
Table-2 Parameters related to Ammonia concentration of 65 (wt. %)
Parameters
Units
Case-1
Case-2
Case-3
Total Flow
TPH
200
300
400
Ammonia
Wt.%
65
65
65
Water
Wt.%
35
35
35
Pump Inlet Pressure
Kg/cm2g
7.6
7.6
7.6
Pump Discharge Pressure
Kg/cm2g
42.4
42.4
42.4
Recuperator Out Temp (Hot stream)
oC
56
59
55
Seperator-1 Inlet
Pressure
Kg/cm2g
40
40
40
Temp
oC
146.3
128.3
120.9
Vap. Fraction
0.47
0.33
0.26
Vapor
Ammonia
Wt.%
93.2
96.8
97.8
Water
Wt.%
6.8
3.2
2.2
Power gen
MW
4.76
4.72
4.74
Heat Duty
MW
39
39
39
Pump Duty
MW
0.329
0.493
0.658
20
Super Heat
MW
0
0
0
Turbine Out
oC
84.1
61.8
51
Vapor %
%
95
96
96
Net Power (Standalone)
MW
4.43
4.23
4.08
Thermal Eff. (Standalone)
%
11.27
10.70
10.29
Energy Saved Due to PRD
MW
0.15
0.29
0.43
Net Power (Including PRD)
MW
4.59
4.52
4.51
Thermal Eff. (Including PRD)
%
11.66
11.44
11.38
Table-3 Parameters related to Ammonia concentration of 70 (wt. %)
Parameters
Units
Case-1
Case-2
Case-3
Total Flow
TPH
200
150
300
Ammonia
Wt.%
70
70
70
Water
Wt.%
30
30
30
Pump Inlet Pressure
Kg/cm2g
8.8
8.8
8.8
Pump Discharge Pressure
Kg/cm2g
42.4
42.4
42.4
Recuperator Out Temp (Hot stream)
oC
58
59
59
Seperator-1 Inlet
Pressure
Kg/cm2g
40
40
40
Temp
oC
136.2
153.8
118.8
Vap. Fraction
0.5
0.62
0.35
Vapor
21
Ammonia
Wt.%
95.5
91
98
Water
Wt.%
4.5
9
2
Power gen
MW
4.49
4.41
4.44
Heat Duty
MW
39
39
39
Pump Duty
MW
0.325
0.244
0.488
Super Heat
MW
0
0
0
Turbine Out
oC
76.9
96.6
53.4
Vapor %
%
96
96
96
Net Power (Standalone)
MW
4.17
4.17
3.95
Thermal Eff. (Standalone)
%
10.59
10.62
10.00
Energy Saved Due to PRD
MW
0.14
0.08
0.28
Net Power (Including PRD)
MW
4.31
4.25
4.23
Thermal Eff. (Including PRD)
%
10.96
10.82
10.70
Table-4 Parameters related to Ammonia concentration of 75 (wt. %)
Parameters
Units
Case-1
Case-2
Case-3
Total Flow
TPH
120
150
200
Ammonia
Wt.%
75
75
75
Water
Wt.%
25
25
25
Pump Inlet Pressure
Kg/cm2g
9.9
9.9
9.9
Pump Discharge Pressure
Kg/cm2g
42.4
42.4
42.4
Recuperator Out Temp
oC
60
60
60
22
(Hot stream)
Separator Inlet
Pressure
Kg/cm2g
40
40
40
Temp
oC
160.7
144.5
125.4
Vap. Fraction
0.75
0.65
0.53
Vapor
Ammonia
Wt.%
88.7
93.6
97.26
Water
Wt.%
11.3
6.4
2.74
Power gen
MW
4.17
4.27
4.28
Heat Duty
MW
39
39
39
Pump Duty
MW
0.193
0.242
0.322
Super Heat
MW
0
0
0
Turbine Out
oC
106.5
89.8
66.4
Vapor %
%
95
93.6
96
Net Power (Standalone)
MW
3.98
4.03
3.96
Thermal Eff. (Standalone)
%
10.14
10.27
10.06
Energy Saved Due to PRD
MW
0.04
0.07
0.13
Net Power (Including PRD)
MW
4.02
4.10
4.09
Thermal Eff. (Including PRD)
%
10.25
10.45
10.40
The impact on efficiency by installing Jacketed pressure recovery device is clearly described in each Table. The modified Kalina cycle of the present disclosure having jacketed pressure recovery device has higher thermal efficiency, higher energy recovered and higher net power on comparison to the 5
23
Kalina cycle without jacketed pressure recovery. The thermal efficiency and the energy recovered are low for the Kalina cycle without jacketed pressure recovery.
Hence, the modified Kalina cycle having Jacketed pressure recovery device according to present disclosure shows higher energy recovery.
Furthermore, from the tables it is evident that the Thermal efficiency decreases 5 with increase in ammonia concentration. But low ammonia concentration suffers from less heat recovery. Though Power generated is low in case of high thermal efficiency for ammonia concentration of 60 wt. %, it should be noted that the exit temperature of heat source is high.
Superheating the vapor can also increase the power generation and better dryness 10 but at the cost of high exhaust temperature ex- turbine. Alternatively, availability of heat source at low quantity at high temperature may also be utilised for super heating.
Example 2: In example 2, the working fluids other than Ammonia-water are studied. Various hydrocarbon mixture can be considered. Table 5 Indicates the 15 parameters related to propylene as Fluid-1 and other Fluids like Butane, Iso Butane, Pentane, Iso-Pentane are Fluid-2. To bring the similarity, Propylene is similar to Ammonia in Ammonia Water working fluid. Fluid-2 is similar to Water.
Table-5: Kalina Cycle with Hydrocarbon mixtures (With major component 20 (Fluid 1) as Propylene)
Parameters
Units
Fluid-2 (Fluid -1 : Propylene)
Butane
Iso Butane
Pentane
Iso Pentane
Total Flow
kg/s
110.00
80.00
80.00
80.00
Fluid-1
Wt.%
85
85
85
85
Fluid-2
Wt.%
15
15
15
15
24
Pump Inlet Pressure
Kg/cm2g
18.7
15
15
15
Pump Discharge Pressure
Kg/cm2g
42.4
42.4
42.4
42.4
Separator Inlet
Pressure
Kg/cm2g
40
40
40
40
Temp
oC
143.2
155
105.4
154.4
Vap. Fraction
1
1
1
1
Power gen
MW
3.065
3.216
2.926
3.116
Heat Duty
MW
38.9
38.9
38.9
38.9
Pump Duty
MW
0.666
0.4979
0.656
0.487
Super Heat
MW
0
0
0
0
Eff
%
6.06
6.90
5.74
6.67
Net Power
MW
2.40
2.72
2.27
2.63
Example 3: In example 3, the working fluid mixture consists of propane as Fluid-1 and other Fluids like Butane, Iso Butane, Pentane, Iso Pentane. are Fluid-2. To bring the similarity, Propane is Similar to Ammonia in Ammonia Water working fluid. Fluid-2 is similar to Water. 5
Table-6 Kalina Cycle with Hydrocarbon mixtures (With major component (Fluid 1) as Propane)
Parameters
Units
Fluid-2 (Fluid -1 : Propane)
Butane
Iso Butane
Pentane
Iso Pentane
Total Flow
kg/s
80.00
80.00
80.00
90.00
Fluid-1
Wt.%
85
85
85
85
Fluid-2
Wt.%
15
15
15
15
Pump Inlet Pressure
Kg/cm2g
12
12
12
12
25
Pump Discharge Pressure
Kg/cm2g
42.4
42.4
42.4
42.4
Seperator-1 Inlet
Pressure
Kg/cm2g
40
40
40
40
Temp
oC
154.5
151.1
123.8
132.7
Vap. Fraction
1
1
1
1
Power gen
MW
3.606
3.646
2.902
3.528
Heat Duty
MW
38.9
38.9
32.4
38.9
Pump Duty
MW
0.5496
0.567
0.554
0.6205
Super Heat
MW
0
0
0
0
Eff
%
7.75
7.80
7.13
7.36
Net Power
MW
3.06
3.08
2.35
2.91
In case of Hydrocarbon Liquids with the Heat source at 170 oC, entire hydrocarbon is vaporised. So only vapour part of the stream goes to the jacketed Pressure recovery device. Here, the intention is to show that based on different working fluid combination and operating temperature, the system can be 5 optimised.
Example 4: In example 4 working fluid mixture consists of alcohols. Methanol (90 wt. %) and Ethanol (10 wt. %). To bring the similarity with Ammonia-Water Kalina Cycle, methanol is Similar to Ammonia in Ammonia Water working fluid. ethanol is similar to Water. 10
Table-7 Kalina Cycle with Alcohol mixtures (With major component (Fluid-1) as methanol)
Parameters
Units
Case-1
Case-2
Total Flow
kg/s
30.00
70.00
26
Methanol
Wt.%
90
90
Ethanol
Wt.%
10
10
Pump Inlet Pressure
Kg/cm2g
1.5
1.5
Pump Discharge Pressure
Kg/cm2g
15
12
Seperator-1 Inlet
Pressure
Kg/cm2g
40
40
Temp
oC
153
150
Vap. Fraction
0.3
0.22
Power gen
MW
0.872
1.148
Heat Duty
MW
13
19.5
Pump Duty
MW
0.06
0.112
Super Heat
MW
0
0
Efficiency (Standalone)
%
6.14
5.26
Net Power (Standalone)
MW
0.80
1.03
Energy Saved Due to PRD
MW
0.13
0.31
Net Power Generated (With PRD)
MW
0.93
1.35
Net Efficiency (With PRD)
%
7.15
6.87
Even by varying the working fluid in examples 2, 3 and 4 it was found that the jacketed pressure recovery device has higher energy recovery and efficiency.
Further, it was found that the Ammonia water system is found to be more efficient in the example considered. 5
27
The Applicability of Pressure recovery device may not be observed in some cases based on the temperature range of the heat source and operating pressure if the total working fluid gets evaporated in the evaporator.
Advantages:
The process and apparatus disclosed in the present invention provides the 5 following advantages:
• Better or efficient energy recovery;
• Energy recovery even from low- temperature source;
• Simple and cost-effective system and process.
10
List of Reference Numerals:
10, 13
Heat source
17
Power input
16
Cold source
101
Heat exchanger/evaporator
102
Gas/liquid separator
103
Superheater
104
Expander/Turbo generator
105
Power output
106
Pressure recovery device (PRD)
110
Jacketed pressure recovery device
107
Condenser
108
Pump
109
Recuperator
15
11
High pressure stream
12
High pressure vapour
14
Super- heated vapour
15
Low pressure saturated vapour
18
High pressure liquid
19
Cooling water supply in 110
20
Cooling water return from 110
21
mixture stream

We Claim:

1. A system for an efficient energy recovery from low temperature heat source, comprising,
a pump to convert a low pressure multi-component working fluid stream into pressurised working fluid; 5
a heat exchanger (101) which partially or completely vaporizes the working fluid to produce high pressure stream (11) by transferring heat from the heat source, which is at a temperature of below 250oC;
a gas/liquid separator (102) which separates a high pressure vapor (12) and a high pressure liquid (18) from the high pressure stream (11); 10
an expander (104) which converts the heat energy from the high pressure vapor (12) to work energy;
a pressure recovery device (110), which increases the pressure of the high pressure liquid (18) and low pressure vapor (15) to produce a mixture stream (21) having a mixture of vapor and liquid phases, 15
characterized in that the pressure recovery device (110) has a converting (A) and diverging (B) section and the either or both of the sections has a jacketed cooling around the periphery, to reduce the temperature and produce the mixture stream (21);
a condenser (107) which converts the vapor phase into liquid phase in the 20 mixture stream (21) by transferring heat to the cold source (16).
2. The system as claimed in claim 1, wherein the jacketed pressure recovery device has single inlet or multiple inlet for cooling water.
3. The system as claimed in claims 1 or 2 wherein, the jacketed pressure recovery device has fins on the ejector side for better heat recovery. 25
4. The system as claimed in claim 1, wherein the temperature of the heat source in in the range of 50oC to 250oC.
5. The system as claimed in claim 1, wherein the high pressure vapor (12) from the separator (102) is passed though a super heater (103) to increase the temperature of the high pressure vapor (12). 30
29
6. The system as claimed in claim 1, where in the expander (104) is a turbine and the work from the expander is converted into electrical energy by electricity generator.
7. The system as claimed in claim 1, where in the pressurised working fluid from the pump (108) is passed through the recuperator (109) to transfer 5 heat from the high pressure liquid (18) to the said pressurised working fluid.
8. The system as claimed in claim 1, wherein the jacketed pressure recovery device (110) is cooled by the cold source.
9. The system as claimed in claims 1 and 7, wherein the cold source is the 10 cooling water.
10. The system as claimed in claim 1, wherein the heat source is a flue gas from gas turbine exhaust, fired equipment like Boilers, furnaces, HRSg process stream or a low-grade heat being wasted to the atmosphere.
11. The system as claimed in claim 1, wherein the working fluid is binary 15 mixture having fluid 1 and fluid 2.
12. The system as claimed in claim 10, wherein the fluid 1 is selected from ammonia, propylene, propane and methanol; the fluid 2 is selected from water, butane, iso butane, pentane, iso-pentane and ethanol.
13. A process for efficient energy recovery from low temperature heat source 20 comprising steps of
pressurising a multi-component low pressure working fluid in a pump (108) to produce pressurised working fluid;
vaporising or exchanging heat from a heat source, which is below 250 oC, to the pressurised working fluid in a heat exchanger (101) to produce a 25 high pressure saturated stream (11);
separating the gas and liquid phase of the high pressure saturated stream (11) in a gas/liquid separator (102) to produce high pressure vapor (12) and high pressure liquid (18);
converting the heat energy from the high pressure vapor (12) to work, in a 30 expander (104) to produce a low pressure saturated vapor (15);
30
recovering pressure of the low pressure saturated vapor (15) and high pressure liquid (18) in a pressure recovery device (110) to produce a mixture stream (21),
characterized in that the pressure recovery device (110) has a jacketed cooling system around the periphery to reduce the temperature and 5 produce the mixture stream (21),
condensing the vapor from the mixture stream (21) to produce the multicomponent low pressure liquid working fluid.
14. The process as claimed in claim 12, wherein the working fluid is binary mixture having fluid 1 and fluid 2. 10
15. The system as claimed in claim 13, wherein the fluid 1 is selected from ammonia, propylene, propane and methanol and the fluid 2 is selected from water, butane, iso butane, pentane, iso-pentane and ethanol.