A cryogenic air separation unit (ASU) with double column configuration produces pressurized oxyge... more A cryogenic air separation unit (ASU) with double column configuration produces pressurized oxygen (PGOX) at purity of 99.6% and above. A single column configuration is sufficient to produce at a purity of 95%, which is required for carbon capture power plants (CCPP). It requires less capital and consumes lower power than a double column configuration. It further makes an economic sense if the unutilized bone-dry low purity (waste) nitrogen, also called pressurised impure gaseous nitrogen (PiGAN), may be heated by the waste heat available in CCPP. It is expanded in a gas-based reheat cycle to produce electricity. This may partially offset the power consumed in the ASU. Using exergy analysis, pressure of PiGAN is determined in such a way that the net power consumed by ASU (power consumed minus power generation in power cycle) is minimized. At this pressure of PiGAN, single column ASU consumes 12.5% less power than double column ASU.
The direct method program SAYTAN has been applied successfully to redetermine the structure of cy... more The direct method program SAYTAN has been applied successfully to redetermine the structure of cytochrome c
LNG cold can be utilized to reduce specific energy consumption (SPC) in an air separation unit (A... more LNG cold can be utilized to reduce specific energy consumption (SPC) in an air separation unit (ASU). LNG cold can be used to produce pressurized gaseous oxygen (PGOX), pressurized gaseous nitrogen (PGAN), liquid oxygen (LOX) and liquid nitrogen (LIN). The proposed configuration is safer than that proposed in a published paper by Tesch et al. (2017) where PGOX is produced by pumping LOX and vapourizing it in main heat exchanger (MHX) instead of getting pressurized in a compressor. Further, we avoid bringing flammable fuel LNG to the ASU premises. Nitrogen from ASU to the regasification terminal gets converted to LIN in a heat exchanger and the same returns to the ASU. Power consumption, the purity of the products, exergy destruction and exergy efficiency are determined by simulating the plant on Aspen Hysys 8.6TM process simulator. The results show that apart from improved safety, the exergy efficiency of the proposed system is higher than that of the configuration compared.
Abstract Liquefied natural gas (LNG) is warmed by seawater in a regasification terminal and the c... more Abstract Liquefied natural gas (LNG) is warmed by seawater in a regasification terminal and the cold energy is usually wasted. Organic Rankine cycle (ORC) has emerged as the preferred thermodynamic cycle to extract green power from LNG using the temperature difference existing between LNG and the environment. The design of ORC based on a fixed temperature difference for all heat exchangers is proposed to be replaced with optimum temperature differences. Simulation with Aspen HYSYS 8.6® shows that the total surface area as obtained with a fixed temperature difference can be optimally redistributed among the heat exchangers to increase extraction of power. A three-stage cascaded ORC with ethane, ethane and propane as the working fluids generated an additional power of 123 kW with LNG vaporising at 30 kg per second without any additional surface area of heat exchangers. The paper further shows that for a delivery pressure at 6 bar(a), additional power of 630 kW can be generated from LNG vaporising at 30 bar(a) and thereafter expanded to 6 bar(a) in a turbine, instead of extracting power from 6 bar(a) LNG. The analysis shows that the third stage generates only 10% and the other two stages contribute equally to power generation.
Cold available with vaporized pumped LNG in regasification terminals is converted to power by an ... more Cold available with vaporized pumped LNG in regasification terminals is converted to power by an Organic Rankine cycle (ORC). The capital cost of an ORC is largely dependent on the surface area of the heat exchangers that are usually designed with a fixed temperature approach or pinch temperature difference. This paper shows that it is possible to increase power production substantially by re-distributing a given total surface area optimally among the heat exchangers that involves no additional cost. The ORC chosen for analysis is a three-stage cascaded cycle whose first two stages are cascaded. Simulation on Aspen HYSYS® V8.6 shows that ORC with optimal allocation of surface area among the heat exchangers can produce 435 kW higher power than that is designed with fixed temperature differences of 5 °C when LNG is pumped, vaporized and delivered at 6 bar(a) at a flow of 30 kg/s. Maximum total and stage-wise powers are calculated for wide range of total heat exchanger surface areas. T...
A cryogenic air separation unit (ASU) with double column configuration produces pressurized oxyge... more A cryogenic air separation unit (ASU) with double column configuration produces pressurized oxygen (PGOX) at purity of 99.6% and above. A single column configuration is sufficient to produce at a purity of 95%, which is required for carbon capture power plants (CCPP). It requires less capital and consumes lower power than a double column configuration. It further makes an economic sense if the unutilized bone-dry low purity (waste) nitrogen, also called pressurised impure gaseous nitrogen (PiGAN), may be heated by the waste heat available in CCPP. It is expanded in a gas-based reheat cycle to produce electricity. This may partially offset the power consumed in the ASU. Using exergy analysis, pressure of PiGAN is determined in such a way that the net power consumed by ASU (power consumed minus power generation in power cycle) is minimized. At this pressure of PiGAN, single column ASU consumes 12.5% less power than double column ASU.
The direct method program SAYTAN has been applied successfully to redetermine the structure of cy... more The direct method program SAYTAN has been applied successfully to redetermine the structure of cytochrome c
LNG cold can be utilized to reduce specific energy consumption (SPC) in an air separation unit (A... more LNG cold can be utilized to reduce specific energy consumption (SPC) in an air separation unit (ASU). LNG cold can be used to produce pressurized gaseous oxygen (PGOX), pressurized gaseous nitrogen (PGAN), liquid oxygen (LOX) and liquid nitrogen (LIN). The proposed configuration is safer than that proposed in a published paper by Tesch et al. (2017) where PGOX is produced by pumping LOX and vapourizing it in main heat exchanger (MHX) instead of getting pressurized in a compressor. Further, we avoid bringing flammable fuel LNG to the ASU premises. Nitrogen from ASU to the regasification terminal gets converted to LIN in a heat exchanger and the same returns to the ASU. Power consumption, the purity of the products, exergy destruction and exergy efficiency are determined by simulating the plant on Aspen Hysys 8.6TM process simulator. The results show that apart from improved safety, the exergy efficiency of the proposed system is higher than that of the configuration compared.
Abstract Liquefied natural gas (LNG) is warmed by seawater in a regasification terminal and the c... more Abstract Liquefied natural gas (LNG) is warmed by seawater in a regasification terminal and the cold energy is usually wasted. Organic Rankine cycle (ORC) has emerged as the preferred thermodynamic cycle to extract green power from LNG using the temperature difference existing between LNG and the environment. The design of ORC based on a fixed temperature difference for all heat exchangers is proposed to be replaced with optimum temperature differences. Simulation with Aspen HYSYS 8.6® shows that the total surface area as obtained with a fixed temperature difference can be optimally redistributed among the heat exchangers to increase extraction of power. A three-stage cascaded ORC with ethane, ethane and propane as the working fluids generated an additional power of 123 kW with LNG vaporising at 30 kg per second without any additional surface area of heat exchangers. The paper further shows that for a delivery pressure at 6 bar(a), additional power of 630 kW can be generated from LNG vaporising at 30 bar(a) and thereafter expanded to 6 bar(a) in a turbine, instead of extracting power from 6 bar(a) LNG. The analysis shows that the third stage generates only 10% and the other two stages contribute equally to power generation.
Cold available with vaporized pumped LNG in regasification terminals is converted to power by an ... more Cold available with vaporized pumped LNG in regasification terminals is converted to power by an Organic Rankine cycle (ORC). The capital cost of an ORC is largely dependent on the surface area of the heat exchangers that are usually designed with a fixed temperature approach or pinch temperature difference. This paper shows that it is possible to increase power production substantially by re-distributing a given total surface area optimally among the heat exchangers that involves no additional cost. The ORC chosen for analysis is a three-stage cascaded cycle whose first two stages are cascaded. Simulation on Aspen HYSYS® V8.6 shows that ORC with optimal allocation of surface area among the heat exchangers can produce 435 kW higher power than that is designed with fixed temperature differences of 5 °C when LNG is pumped, vaporized and delivered at 6 bar(a) at a flow of 30 kg/s. Maximum total and stage-wise powers are calculated for wide range of total heat exchanger surface areas. T...
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Papers by Kanchan Chowdhury