The present disclosure relates to a field of recovery of waste thermal energy. Particularly, the disclosure relates to an efficient, self-sustaining process for recovery of energy from heat source and improving efficiency by reducing fuel consumption. More particularly, the disclosure relates to a process involving a thermodynamic cycle for recovery of heat or thermal energy, which is self-sustaining i.e. it does not require external sources. The process of the present invention is highly integrated such that the required energy and utility for the process is available/ produced in the process. The present disclosure also relates to a self-sustained system for converting a thermal energy from heat sources into power.
BACKGROUND OF THE INVENTION:
Process industries are generally energy intense. Various streams in the process industries are at high temperatures and involve thermal energy. In the design of a process plant, an attempt is generally made to recover most of the process heat for use within the plant. However, heat at low temperatures and heat of exhaust gases are generally lost to the atmosphere or to cooling water (through air or water coolers and condensers) for which no alternate use is found. This quantity of waste heat which is lost adds up to a substantial amount in a typical facility. Process schemes to tap this low-level heat are feasible and provide the additional benefit of reduced capital investment and energy input. Energy recovery and utilization from these streams not only reduces the energy consumption, but also reduces environmental pollution and achieves energy saving effect. The streams can be of low temperature heat source or a high temperature source.
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 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 exchange. These low temperature, low grade heat are abundant in the industry and find no application in the industry.
High temperature heat source usually refers to streams with temperature above 200°C, typically in the range of 250 to 500°C. These streams have high amount of energy in it and recovering the same is essential to reduce the overall energy consumption.
Both the low and high 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 energy streams possess a lot of energy. Various process schemes are used to recover the energy from the heat sources.
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 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 66°C to 260°C and may be used from ambient to its critical temperature. A working fluid of lower volatility is preferred for stages at higher temperature and a more volatile working fluid for the stages at lower temperature.
Further, in the US patent publication US20060236698A1, waste heat recovery from the low heat source having 140 ° F. to about 300 ° F and converting the heat to work by thermodynamic process is disclosed. The US patent no. US 9,708,973 B2 is directed to the field of power generation system utilizing waste heat from a reformer system. The US patent no US 9,725, 652 B2 described a combined heat and power generation system for use with a delayed coking plant.
There are many other process schemes for recovering the low-level heat such us Boiler feed water heating in which the temperature of make-up water is increased

to reduce the fuel cost in the boiler. This scheme has limited use due to the requirement of boiler feed water. All the prior arts disclose the use of energy and utility from the outside source. There is a requirement for the utility source in the above documents, for the recovery system to function properly. Thus, there is a need to improve the heat recovery process such that the process is self-sustaining, that does not require external utility and energy to function.
Although the prior arts disclose various process schemes to recover heat from low temperature streams, the systems or schemes know are either very complex and has dependency on other system for utilities such as cooling water and power . There is a need for a method and apparatus for self sustained system that is nondependent on other systems and self sustainable system for conversion of heat to power from standalone heat sources..
So, there is a requirement for a process scheme which produces more work/ improved energy conversion efficiency. The present invention provides such a method and apparatus.
In view of this, the inventor of the present disclosure felt a need to develop a process which overcomes all the problems of the prior arts and is self- sustained. Particularly there is a need to improve the efficiency and dependency of the process schemes. The present invention provides a self-sustaining process for recovering the waste heat rejected to air/cooler and/or water cooler and in atmosphere in form of exhaust gases etc. This self-sustaining process increases efficiency by recovering waste heat and reducing fuel consumption in typical facility. The process not only gives economic benefit but also addresses the environmental aspect for reducing the greenhouse gases.
SUMMARY OF THE INVENTION:
The present disclosure relates to a process for recovery of energy from a heat source. Particularly, the disclosure relates to a process scheme that converts the thermal energy from the heat source to the mechanical energy. The process scheme 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 an efficient, self-sustaining process for recovery of energy from heat source. The process and system of the instant invention is self-sustaining i.e. does not require external sources. The process of the present invention is highly integrated such that the required energy and utility for the process is available/ produced in the process.
The present invention is for recovery of both low level and high-level heat from process industries. Recovery of low-level heat can rarely be considered by looking at an individual source in isolation. It is necessary to interlink units wherein low-level heat can be recovered to the maximum extent. This is especially true for plants which have several sub-units supplied by different process technology providers. Moreover, the present invention is also for recovering and utilization of waste heat lost in hot exhaust gases to atmosphere from isolated source such as standalone compression systems.
In further aspect of the present disclosure, a system for efficient energy recovery is disclosed. The system involves transferring heat from the heat source to the working fluid, converting the heat into work without need to external utility.
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 conjunction with drawings, wherein
Figure 1 is the process flow diagram of low-level waste heat recovery in Process Industries using self-sustaining process of the invention.
Figure 2 is the process flow diagram of waste heat recovery from GT Exhaust using self-sustaining process of the invention.
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
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
5 that the examples are mentioned to show only those specific details that are
pertinent to understanding the aspects of the present 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 provides a self-sustained process and system for
10 recovering both low level heat and high-level heat in process industries. The
streams in the range of 120 – 250 °C, generally lost to the atmosphere or to
cooling water (through air or water coolers and condensers) are considered as
low-level heat. The self-sustaining process scheme utilizes a hydrocarbon or
mixtures of hydrocarbon as a heat transfer medium to recover waste heat from the
15 process units. The low-temperature heat is converted into useful work that can
itself be converted into electricity.
The present invention also provides process for waste heat recovery from isolated heat source such as exhaust gases at standalone Gas compression station. In Gas
20 compression facility high temperature exhaust gases are released from gas
turbines. The temperature of exhaust gases is in the range of 250-500 oC. This heat is lost in atmosphere. The self-sustaining process disclosed here is capable of recovering process heat from exhaust gases. In a typical facility this self-sustaining process generates net power 2-3 MW. This power is utilized to run one
25 of the compressors.
The invention provides a better system for efficient energy recovery from the low temperature energy source. This is achieved by using a thermodynamic cycle which is self-sustained and efficient.
30 In one particulate embodiment, the disclosure relates to a self- sustaining process
for efficient energy recovery from heat source comprising steps of
6

pressurising a low-pressure working fluid in a pump (P-01, P1) to produce pressurised working fluid;
vaporising or exchanging heat from a heat source in exchangers (EE-01, EE-02,
E1, E2, E3, E4) to produce a high-pressure saturated stream;
5 converting the heat energy from the high-pressure saturated stream to work, in an
expander (K-01, K1) to produce a low pressure saturated vapor;
condensing the low pressure saturated vapor in a condenser (AC-01, AC1) to
produce the low-pressure liquid characterized in that the power required for the
pump and the utility for the condenser is obtained from the work produced from
10 the expander resulting in a highly integrated process.
In another embodiment of the invention, the utility required for system and process for recovering waste heat and generating power is generated in the process itself.
15
In yet another embodiment of the invention, the working fluid is an organic fluid having low boiling temperature and it is vaporized during the exchange of heat and vapour is expanded to generate power such as hydrocarbons or mixture of hydrocarbons. .
20
In yet another embodiment of the invention, the temperature of the heat source (EE-01, EE-02) in in the range of 120oC to 250oC and the low level heat recovered is for power generation in the process industries.
25 In yet another embodiment of the invention, the temperature of the heat source
(E1, E2, E3, E4) is greater than 250 oC and in the range of 300oC to 500oC,wherein the waste heat recovered from exhaust gases at gas compression station.
30 In yet another embodiment of the invention, the power generated is used to run
the compressor and fuel gas consumption is reduced.
In yet another embodiment of the invention, the heat source is a flue gas from gas turbine exhaust, exhaust gases from compression station, fired equipment like
7

Boilers, furnaces, HRSG process stream or a low-grade heat being wasted to the atmosphere in process industries.
Another embodiment of the invention relates to a self-sustained system for
5 recovery of heat from the heat source, comprising,
a pump (P-01, P1) to convert a low-pressure working fluid stream into
pressurised working fluid;
the pressurized working fluid is vaporized to produce high pressure vapour
stream by exchanging heat from the heat source in exchangers (EE-01, EE-02,
10 E1,E2,E3,E4);
an expander (K-01, K1) which converts the heat energy from the high pressure
vapor to work energy and produces a low pressure vapor;
a condenser (AC-01, AC1) which condenses the low pressure vapor to form
liquid.
15 characterized in that the power for the pump and the utility for the condenser is
obtained from the work produced from the expander resulting in a highly
integrated system.
In yet another embodiment of the invention, the temperature of the heat source is
20 the range of 120oC to 500oC.
In yet another embodiment of the invention, the expander (K-01, K1) is a turbine and the work from the expander is converted into electrical energy by electricity generator.
25
In yet another embodiment of the invention, the heat source (EE-01, EE-02,E1,E2,E3,E4) 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.
30
In yet another embodiment of the invention, the working fluid is hydrocarbons or mixture of hydrocarbons such as butane, pentane etc.
8

The typical process conditions of low-level heat stream available in process units are given in Table -1.
Table 1: Typical low-level heat streams available in Process Units

Process units Temperature, °C Recoverable duty, MMkcal/hr
Unit 1 190 9.0
Unit 2 170 6.0
As an existing system, the product rundowns are available at 190 °C / 170 °C
5 which reject their heat to air cooler and / or water cooler. The present invention
recovers this valuable low-level heat for generating power. The working which is organic fluid such as hydrocarbons or mixture of hydrocarbons is pumped to the process units, where the working fluid exchanges the available low level heat in the product rundowns in exchangers (EE-01, EE-02) and working fluid gets
10 vaporized. The vaporized high pressure working fluid is expanded in turbine to
generate power and the expanded working fluid, which is at vapor phase, is then condensed in a cooler.
Based on the heat available (~15 MMkcal/hr which equals to 17.3 MW) in the product rundowns of Process unit-1 and Process unit-2, the self-sustaining
15 process can generate a Net output of approx. 1.3 MW (Electrical Power net of
working fluid pump, and aircooler).
The system and process of the present disclosure is designed to operate with a both single and multi-component working fluid. The working fluid is preferably
20 hydrocarbons or multi-component fluid that comprises mixtures of hydrocarbons.
The working fluid must have necessary thermo-physical properties that match the application but also possess adequate chemical stability in desired temperature range. In certain embodiments, the working fluids include mixture, a mixture of two or more hydrocarbons, a mixture of two or more class of refrigerants, a
25 mixture of hydrocarbons and class of refrigerants, or the like. In general, the fluid
can comprise mixtures of any number of compounds with favourable thermodynamic characteristics and solubility.
9

Referring to Fig.1 which illustrates the process of the invention. As an existing system, the product rundowns are available at 190 °C / 170 °C which reject their heat to aircooler and / or water cooler. A self-sustaining process scheme is developed to recover this valuable low-level heat for generating power.
5 A working fluid is circulated in the entire system for exchanging heat with the
desired process units. The low-level heat streams from the process units I and II transfers heat to the working fluid.
A working fluid must not only have the necessary thermo-physical properties that
match the application but also possess adequate chemical stability in the desired
10 temperature range. The fluid selection affects system efficiency, operating
conditions, environmental impact and economic viability and availability. Butane, pentane etc are used as working fluid.
The low-level heat available in the Process unit-I (X1) and Process unit –II (X2)
are 9 MMkcal/hr and 6 MMkcal/hr, respectively. The working fluid is pumped to
15 the process units, exchanges the available low level heat in the product rundowns
in exchangers (E-01, E-02) and the working fluid gets vaporized. The vaporized high-pressure working fluid is expanded in turbine (K-01) to generate power and the expanded working fluid, which is at vapor phase and is condensed in a air cooler (AC-01).
20 Based on the heat available (~15 MMkcal/hr which equals to 17.3 MW) in the
product rundowns of Process unit-1 and Process unit-2, the self sustaining process can generate a Net output of approx. 1.3 MW (Electrical Power net of Thermic Fluid Pump, working fluid pump, and water condenser pump).
Referring to Fig.2 which also illustrates the process of the invention. In gas
25 pipeline network, there is compression system which is run by gas turbines; the
exhaust of gas turbines is released to atmosphere. The heat from this exhaust can
be utilized for "clean" power generation employing waste heat recovery systems.
A self-sustaining process scheme is developed to recover this valuable waste heat
for generating power. Hydrocarbons and mixture of hydrocarbons such as
30 Butane, Pentane etc. are used as working fluid for heat transfer.
10

The Exhaust gases are at temperatures 250-500oC. Working fluid is vaporized in
exchangers E1, E2, E3 and E4 using available exhaust gases. The vaporized high-
pressure working fluid is expanded in expander (K1) to generate power and the
expanded working fluid, which is at vapor phase and is condensed in an air cooler
5 (AC1). Then, it is pumped to exchangers E1, E2, E3, E4 using pump P1. In a
typical facility approximately 2 MW power is generated based on waste heat available.
The closed-circuit heat recovery apparatus of the present disclosure comprises an
Exchangers (EE-01, EE-02, E1, E2, E3, E4), an expander (K-01, K1), a
10 condenser (AC-01, AC1) and a pump (P-01, P1), wherein
a) The expander (K-01, K1) 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 such work, said expander being in fluid communication with said exchangers;
15 b) The condenser (AC-01,AC1) has a heat exchanger for generating liquid
working fluid by transferring heat from the working fluid to atmosphere to condense the working fluid, said condenser being in fluid communication with said pump, and
c) The pump (P-01, P1) is for raising the pressure and for pumping the liquid
20 from the condenser to exchangers; said pump being in fluid communication with
said condenser and said exchangers
f) The exchangers (EE-01,EE-02,E1,E2,E3,E4) has a heat exchanger for evaporating liquid working fluid by transferring heat from heat sources, said exchangers being in fluid communication with said pump and said expander;
25 The process and system of the present disclosure is self-sustained and efficient.
The heat recovery process of the present disclosure functions in an independent way without the need to external utility sources. The energy required for the working fluid pump, and condenser is taken from the expander. The process is highly integrated, in such a way that the energy requirement is met from with the
30 process. Such high integration results in increased efficiency and reduced fuel
consumption.
11

Although the description mentions all the devices/equipments being involved in the process, any modification of the flow by bypassing the equipment is also within the scope of the invention. The splitting valve and the mixing valve can also be placed in the process to partially pass the stream through the equipment.
5 Examples:
The present invention is now described by way of the following non-limited example:
Example 1: Example 1 comprises the low-level waste heat recovery from heat sources available from process units at typical refinery. The operating conditions
10 of the process scheme such as flow rate, pressure and temperature are listed in the
tables below. The Heat sources available at low level heat available at process units in a typical refinery. Various parameters like temperature, pressure at inlet of pump to maintain working fluid in liquid state, turbine exhaust temperature, pressure to be maintained in the system plays a key role and some are listed in the
15 following table.
Table 1 Low level waste heat recovery at typical refinery process units.

Process Parameters Low Level Waste Heat Case (KW)
Working fluid flow, TPH 140
Hot stream inlet temperature, °C 180
Hot stream outlet temperature, °C 97
Low lever heat recovered, KW 17.4
Expander Inlet Pressure, kg/cm2a 9.5
Expander Outlet Pressure, kg/cm2a 3.0
Expander inlet Temperature,°C 120
Expander outlet Temperature,°C 94
Expander Power Output, KW 1195
Condenser Power consumption, KW 55.2
Pump Power consumption, KW 80
Net Power Output, KW 1060
12

The power generated by the stand-alone heat recovery process is summarized in the table above. The self sustaining process of the present disclosure has recovered energy with nil utilities requirement. The pump and condenser power are provided by process itself.
5 Hence, the process according to present disclosure is self sustainable energy
recovery process.
Example 2: Example 2 comprises the waste heat recovery from GT exhaust
available at typical Gas compression system. The operating conditions of the
process scheme such as flow rate, pressure and temperature are listed in the tables
10 below. The Heat sources available at typical gas compression system. Various
parameters like temperature, pressure at inlet of pump to maintain working fluid in liquid state, turbine exhaust temperature, pressure to be maintained in the system plays a key role and some are listed in the following table.
Table-2 Waste Heat Recovery from GT Exhaust at typical Gas compression
15 system

Process Parameters Waste heat recovery from GT Exhaust (KW)
Working fluid flow, TPH 230
Hot stream inlet temperature, °C 400-500
Hot stream outlet temperature, °C 120
Low lever heat recovered, KW 30.2
Expander Inlet Pressure, kg/cm2a 9.5
Expander Outlet Pressure, kg/cm2a 3.0
Expander inlet Temperature, °C 150
Expander outlet Temperature, °C 124
Expander Power Output, KW 2300.0
Aircooler Power consumption, KW 99.2
Pump Power consumption, KW 120
Net Power Output, KW 2081
The power generated by the stand-alone heat recovery process is summarized in the table above. The self-sustaining process of the present disclosure has
13

recovered energy with nil utilities requirement. The pump and condenser power are provided by process itself. Power generated here is used to run one of the compressors from typical gas compression system, which results in reduction in fuel consumption.
Hence, the process according to present disclosure is self sustainable energy recovery process.
Comparative example l:The process for the comparative example is carried out in the same way as in the example 1, with the exception of the_energy for the pump and utility for condenser is provided from an external source. The calculation for the same is provided in the table below.

Process Parameters Low Level Waste Heat Case (KW)
Working fluid flow, TPH 140
Hot stream inlet temperature, °C 180
Hot stream outlet temperature, °C 97
Low lever heat recovered, KW 17.4
Expander Inlet Pressure, kg/cm2a 9.5
Expander Outlet Pressure, kg/cm2a 3.0
Expander inlet Temperature,°C 120
Expander outlet Temperature,°C 94
Expander Power Output, KW 1195
Condenser Power consumption, KW 55.2
Pump Power consumption, KW 80
It is clearly seen that the energy for the Condenser and the pump (143.2 KW) of energy has to be provided from an external source, which leads to additional fuel consumption. The highly integrated process of the invention eliminated the need for external fuel and the energy need for the process is utilized from the process itself.

Advantages:
The process and apparatus disclosed in the present invention provides the following advantages:
• Self-sustaining, there are no additional utilities are required to run the process;
• Reduces fuel consumption;
• Economical and efficient.
• The process is useful for recovering the low-level heat which is otherwise disposed-off to atmosphere;
• The process is also for recovering waste heat from exhaust gases.
NOMENCLATURE

Numeral Reference
EE-01 Heat source 1
EE-02 Heat source 2
El Heat source - GT exhaust 1
E2 Heat source - GT exhaust 2
E3 Heat source - GT exhaust 3
E4 Heat source - GT exhaust 4
AC-01, AC1 Condenser
P-01,P1 Working fluid pump
K-01,K1 Expander

We Claim:

A self- sustaining process for efficient energy recovery from heat source comprising steps of,
pressurising a low-pressure working fluid in a pump (P-01, PI) to produce pressurised working fluid;
vaporising or exchanging heat from a heat source in exchangers (EE-01, EE-02, E1,E2,E3,E4) to the pressurised working fluid, to produce a high-pressure saturated stream;
converting the heat energy from the high-pressure saturated stream to work, in an expander (K-01, Kl) to produce a low pressure saturated vapor;
condensing the low pressure saturated vapor in a condenser (AC-01, AC1) to produce the low-pressure liquid,
characterized in that, the power required for the pump and the utility for the condenser is generated from the work produced in the expander resulting in a highly integrated process.
The process as claimed in claim 1, wherein the utility required for system and process for recovering waste heat and generating power is generated in the process itself.
The process as claimed in claim 1, wherein the working fluid is an organic fluid having low boiling temperature and it is vaporized during the exchange of heat and vapour is expanded to generate power such as hydrocarbons or mixture of hydrocarbons.
The process as claimed in claim 1, wherein the temperature of the heat source in in the range of 120°C to 250°C and the low level heat recovered is for power generation in the process industries.
The process as claimed in claim 1, wherein the temperature of the heat source is greater than 250 °C and in the range of 250°C to 500°C, wherein the waste heat recovered from exhaust gases at gas compression station. The process as claimed in 1, wherein power generated is used to run the compressor and fuel gas consumption is reduced.
The process as claimed in claim 1, wherein the heat source is a flue gas from gas turbine exhaust, exhaust gases from compression station, fired

equipment like Boilers, furnaces, HRSG process stream or a low-grade
heat being wasted to the atmosphere in process industries.
A self-sustained system for recovery of heat from the heat source,
comprising,
a pump (P-01, PI) to convert a low-pressure working fluid stream into
pressurised working fluid;
the pressurized working fluid is vaporized to produce high pressure
vapour stream by exchanging heat from the heat source in exchangers
(EE-01, EE-02, El, E2, E3,E4);
an expander (K-01, Kl) which converts the heat energy from the high
pressure vapor to work energy and produces a low pressure vapor;
a condenser (AC-01, AC1) which condenses the low pressure vapor to
form liquid,
characterized in that the power for the pump and the utility for the
condenser is generated from the work produced in the expander resulting
in a highly integrated system.
The system as claimed in claim 8, wherein the temperature of the heat
source in in the range of 120°C to 500°C. . The system as claimed in claim 8, where in the expander is a turbine and
the work from the expander is converted into electrical energy by
electricity generator. . The system as claimed in claim 8, 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. . The system as claimed in claim 8, wherein the working fluid is organic
liquid such as hydrocarbons or mixture of hydrocarbons.