Dennis Lu - Academia.edu (original) (raw)

Papers by Dennis Lu

Energy & Fuels, Dec 13, 2017

Chemical Engineering Science, Oct 1, 2023

Energy & Fuels, May 17, 2023

Applied Energy, Dec 1, 2016

Energy & Fuels, Dec 6, 2018

A series of experiments were carried out in a pressurized thermogravimetric analyzer to study the... more A series of experiments were carried out in a pressurized thermogravimetric analyzer to study the effects of H2S on the reactivity of ilmenite oxygen carrier under pressurized conditions. The total...

Proceedings of the Combustion Institute, 2019

O 2 /H 2 O combustion, as a new evolution of oxy-fuel combustion, has gradually gained more atten... more O 2 /H 2 O combustion, as a new evolution of oxy-fuel combustion, has gradually gained more attention recently for carbon capture in a coal-fired power plant. The physical and chemical properties of steam e.g. reactivity, thermal capacity, diffusivity, can affect the coal combustion process. In this work, the ignition and volatile combustion characteristics of a single lignite particle were first investigated in a fluidized bed combustor under O 2 /H 2 O atmosphere. The flame and particle temperatures were measured by a calibrated two-color pyrometry and pre-buried thermocouple, respectively. Results indicated that the volatile flame became smaller and brighter as the oxygen concentration increased. The ignition delay time of particle in dense phase was shorter than that in dilute phase due to its higher heat transfer coefficient. Also, the volatile flame was completely separated from particles (defined as off-flame) in dense phase while the flame lay on the particle surface (defined as on-flame) in dilute phase. The self-heating of fuel particles by on-flame in dilute phase was more obvious than that in dense phase, leading to earlier char combustion. At low oxygen concentration, the flame in the H 2 O atmosphere was darker than that in the N 2 atmosphere because the heat capacity of H 2 O is higher than that of N 2. With the increase of oxygen concentration, the flame temperature in the O 2 /H 2 O atmosphere was dramatically enhanced rather than that in the O 2 /N 2 atmosphere, where the diffusion rate of oxygen in O 2 /N 2 atmosphere became the dominant factor.

Applied Energy, Jun 1, 2017

Social Science Research Network, 2022

Powder Technology, 2016

Abstract A pneumatic conveying system has been designed for the continuous conveying of pulverize... more Abstract A pneumatic conveying system has been designed for the continuous conveying of pulverized fuels, namely biomass (in the form of Canadian forestry waste), lignite, and petroleum coke, to an entrained flow gasification unit. All three fuels studied exhibit properties that are challenging for fluidization or conveying. The lignite and petroleum coke are Geldart class C particles and are expected to exhibit difficulties in conveying, while the biomass is a Geldart class A particle but the non-uniform particle shape and large size distribution result in pneumatic conveying challenges similar to class C particles. The conveying system consists of a blow vessel with three points of gas injection to aerate the bed of material and facilitate hopper discharge. The mass flux of each material was studied as the system parameters were varied, which included: fluidizing and sparge gas (two of the three gases aerating the hopper bed), transfer gas (gas injected directly into the solid transfer line), pressure drop, conveying gas type and transfer line diameter. Fuel fluxes were varied in a range of 450 kg/m2s to 1700 kg/m2s for all three fuels. Compared to lignite and petroleum coke conveying, biomass conveying was found to have a smaller gain in mass flux to many conveying parameters investigated. Additionally, several models for pneumatic conveying of powders were compared against the data obtained. The models were found to have various degrees of relative error, with the best fitting model having a relative error of less than 10% for all three fuels with a marginal bias towards underestimation.

Powder Technology, Apr 1, 2016

International Journal of Energy for a Clean Environment, 2008

ACS omega, Apr 23, 2020

The reactivity of ilmenite as an oxygen carrier (OC) in the presence of H 2 S was studied. A simu... more The reactivity of ilmenite as an oxygen carrier (OC) in the presence of H 2 S was studied. A simulated syngas (66% CO, 34% H 2) was used as the fuel. H 2 S concentrations were set to 4700 and 6580 ppm. The effect of the presence of CO 2 was also investigated. The experiments were carried out using a thermogravimetric analyzer (TGA) at atmospheric pressure, with temperatures varying from 1073 to 1223 K. The results showed that the presence of H 2 S had no effect on the reduction kinetics of ilmenite. With the presence of only CO 2 in the syngas, deposition on ilmenite samples was not observed. In the presence of H 2 S, deposition was observed regardless of the presence of CO 2. Higher H 2 S concentration led to more pronounced deposition. It was shown that deposition only occurred after the ilmenite sample was sufficiently reduced. For ilmenite oxidation, the mass change curves display a distinct peak followed by a valley when the sample was previously reduced in the presence of H 2 S, indicating reactions between the sulfur deposit and air. The amount of the sulfur deposit could be calculated using the oxidation curves. Scanning electron microscope-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) analyses were conducted to examine the surface of the reduced samples and the results from these analyses confirmed the presence of the sulfur deposit on the surface of the samples that were reduced in H 2 S-containing atmospheres.

Absorption processes for CO2 separation employing solid sorbents such as limestone appear to be t... more Absorption processes for CO2 separation employing solid sorbents such as limestone appear to be technically feasible and cost effective. At appropriate temperature and pressure, CO2 from flue gas stream is absorbed by CaO-based sorbent via the carbonation reaction, and the sorbent is then regenerated in a separate reactor and a nearly pure CO2 stream is produced suitable for industrial use or ultimate sequestration. This technology has now been demonstrated using the CANMET pilot-scale dual-fluidized bed system. Havelock limestone from eastern Canada, was used as the CO2 sorbent, while a synthesis gas mixture of air and CO2 (15％) was employed to represent combustion flue gas. Oxy-fuel combustion of biomass and coal was employed in the sorbent regenerating step, creating a high CO2 concentration off-gas stream suitable for sequestration. Pure O2 was mixed with recycled off-gas and this along with the excellent heat transfer characteristics of fluidized bed allowed us to use an O2 ratio of 40％ in the combustion gas. In addition, samples were characterized for pore distribution (nitrogen adsorption/desorption: BET and BJH) and skeleton characterization (density by He pycnometry), as well as changes in sample volume during hydration (sample swelling). The results obtained showed successful hydration even for hydration periods as short as 15 min, and very favorable sample properties. Their pore surface area, pore volume distribution and swelling during hydration are very promising with regard to their use in additional CO2 capture cycles or SO2 retention.

Powder Technology, Oct 1, 2020

International Journal of Greenhouse Gas Control, 2019

A great effort is still pending in terms of thorough bottom-up economic assessments in the partic... more A great effort is still pending in terms of thorough bottom-up economic assessments in the particular case of Chemical Looping Combustion (CLC) and Pressurized Chemical Looping Combustion (PCLC) processes. This work tries to reduce this knowledge gap through a comprehensive techno-economic analysis of PCLC technology focused on the replacement of a Once-through Steam Generator (OTSG) for the production of steam in a Steam Assisted Gravity Drainage (SAGD) facility in Alberta (Canada) by a PCLC system that burns natural gas using ilmenite as oxygen carrier. The evaluation of capital expenditure (CAPEX) for the different CLC cases analyzed revealed that the main contribution to costs stemmed from the rotating equipment. The economic performance of the CLC processes was evaluated through the Levelized Cost of Steam (LCOS) and the cost of CO 2 captured. These parameters ranged between 30.45 and 39.93 CAD/t of steam (23.61-30.95 USD/t) and between 44.39 and 107.05 CAD/t of CO 2 (34.41-82.98 USD/t), respectively. In the particular case of the CLC unit that operated at atmospheric pressure, the results were 34.92 CAD/t of steam (27.07 USD/t) and 75.46 CAD/t of CO 2 (58.50 USD/t), which highlighted the economic benefits resulting from the use of CLC technology under pressurized conditions. Finally, comparing the economic results obtained in this framework with those found in the literature using other Carbon Capture and Storage (CCS) technologies, it can be concluded that PCLC technology has the potential to be a competitive CO 2 capture option in the future for use in industrial SAGD facilities.

International Journal of Greenhouse Gas Control, 2018

International Journal of Greenhouse Gas Control, 2019

Chemical looping reforming is a promising option for the conversion of gaseous fuels to high qual... more Chemical looping reforming is a promising option for the conversion of gaseous fuels to high quality syngas suitable for gas-to-liquids (GtL) processes. This work evaluates the potential for syngas, heat, power, and steam generation for diluent production at steam assisted gravity drainage (SAGD) facilities using low cost ilmenite ore pressurized chemical looping reforming (PCLR). Preliminary fixed-bed reactor testing on a naturally occurring Canadian ilmenite ore was performed to determine the optimal operating regime for syngas generation. Based on SEM characterization, EDX elemental mapping, XRD, and Mössbauer spectroscopy measurements it was demonstrated that partial reduction to Fe 2.5+ and Fe 2+ containing species is required to avoid the production of CO 2. Additionally, the reduction to Fe°containing species should be minimized to limit the formation of carbon and metal carbides. These results were used to generate material and energy balances via Aspen HYSYS V9 process simulation software of the entire PCLR process for SAGD applications using a Canada's Oil Sands Innovation Alliance (COSIA) SAGD facility template. Thorough energy integration of the combined PCLR-SAGD process using Pinch Analysis suggests that steam and diluent requirements can be met, with excess power generation, at lower costs than more traditional syngas generation technologies, while meeting CO 2 emissions targets and reducing boiler feed water (BFW) make-up. Having shown that process performance is attractive, a techno-economic assessment to establish the most economical design for the PCLR-SAGD process is now required.

Energy technology, May 24, 2016

Chemical Engineering Journal

Fuel Processing Technology

The co-combustion of a high-sulphur lignite and biomass blend (up to 50% by weight) has been stud... more The co-combustion of a high-sulphur lignite and biomass blend (up to 50% by weight) has been studied in a small oxy-fired circulating fluidized bed combustion (CFBC) pilot plant. Here the goal is to examine the effect of biomass share on NO x , SO 2 and CO emissions. In these tests, a series of runs has looked at the effect of increasing biomass share under air firing, followed by tests in oxyfiring mode. The results show that the emissions are remarkably insensitive to the biomass share, and are comparable to other results for coal combustion, and likely to be well below any current emission guidelines. Overall, there appear to be no direct challenges to oxy-fuel co-firing in terms of gaseous emissions, although the simple lack of studies means that significantly more data are required on CFBC oxy-firing using a much wider range of biomass and coal types. K doping was also examined and did not result in significant formation of K phases on deposit probes.

Energy & Fuels, Dec 13, 2017

Chemical Engineering Science, Oct 1, 2023

Energy & Fuels, May 17, 2023

Applied Energy, Dec 1, 2016

Energy & Fuels, Dec 6, 2018

A series of experiments were carried out in a pressurized thermogravimetric analyzer to study the... more A series of experiments were carried out in a pressurized thermogravimetric analyzer to study the effects of H2S on the reactivity of ilmenite oxygen carrier under pressurized conditions. The total...

Proceedings of the Combustion Institute, 2019

O 2 /H 2 O combustion, as a new evolution of oxy-fuel combustion, has gradually gained more atten... more O 2 /H 2 O combustion, as a new evolution of oxy-fuel combustion, has gradually gained more attention recently for carbon capture in a coal-fired power plant. The physical and chemical properties of steam e.g. reactivity, thermal capacity, diffusivity, can affect the coal combustion process. In this work, the ignition and volatile combustion characteristics of a single lignite particle were first investigated in a fluidized bed combustor under O 2 /H 2 O atmosphere. The flame and particle temperatures were measured by a calibrated two-color pyrometry and pre-buried thermocouple, respectively. Results indicated that the volatile flame became smaller and brighter as the oxygen concentration increased. The ignition delay time of particle in dense phase was shorter than that in dilute phase due to its higher heat transfer coefficient. Also, the volatile flame was completely separated from particles (defined as off-flame) in dense phase while the flame lay on the particle surface (defined as on-flame) in dilute phase. The self-heating of fuel particles by on-flame in dilute phase was more obvious than that in dense phase, leading to earlier char combustion. At low oxygen concentration, the flame in the H 2 O atmosphere was darker than that in the N 2 atmosphere because the heat capacity of H 2 O is higher than that of N 2. With the increase of oxygen concentration, the flame temperature in the O 2 /H 2 O atmosphere was dramatically enhanced rather than that in the O 2 /N 2 atmosphere, where the diffusion rate of oxygen in O 2 /N 2 atmosphere became the dominant factor.

Applied Energy, Jun 1, 2017

Social Science Research Network, 2022

Powder Technology, 2016

Abstract A pneumatic conveying system has been designed for the continuous conveying of pulverize... more Abstract A pneumatic conveying system has been designed for the continuous conveying of pulverized fuels, namely biomass (in the form of Canadian forestry waste), lignite, and petroleum coke, to an entrained flow gasification unit. All three fuels studied exhibit properties that are challenging for fluidization or conveying. The lignite and petroleum coke are Geldart class C particles and are expected to exhibit difficulties in conveying, while the biomass is a Geldart class A particle but the non-uniform particle shape and large size distribution result in pneumatic conveying challenges similar to class C particles. The conveying system consists of a blow vessel with three points of gas injection to aerate the bed of material and facilitate hopper discharge. The mass flux of each material was studied as the system parameters were varied, which included: fluidizing and sparge gas (two of the three gases aerating the hopper bed), transfer gas (gas injected directly into the solid transfer line), pressure drop, conveying gas type and transfer line diameter. Fuel fluxes were varied in a range of 450 kg/m2s to 1700 kg/m2s for all three fuels. Compared to lignite and petroleum coke conveying, biomass conveying was found to have a smaller gain in mass flux to many conveying parameters investigated. Additionally, several models for pneumatic conveying of powders were compared against the data obtained. The models were found to have various degrees of relative error, with the best fitting model having a relative error of less than 10% for all three fuels with a marginal bias towards underestimation.

Powder Technology, Apr 1, 2016

International Journal of Energy for a Clean Environment, 2008

ACS omega, Apr 23, 2020

The reactivity of ilmenite as an oxygen carrier (OC) in the presence of H 2 S was studied. A simu... more The reactivity of ilmenite as an oxygen carrier (OC) in the presence of H 2 S was studied. A simulated syngas (66% CO, 34% H 2) was used as the fuel. H 2 S concentrations were set to 4700 and 6580 ppm. The effect of the presence of CO 2 was also investigated. The experiments were carried out using a thermogravimetric analyzer (TGA) at atmospheric pressure, with temperatures varying from 1073 to 1223 K. The results showed that the presence of H 2 S had no effect on the reduction kinetics of ilmenite. With the presence of only CO 2 in the syngas, deposition on ilmenite samples was not observed. In the presence of H 2 S, deposition was observed regardless of the presence of CO 2. Higher H 2 S concentration led to more pronounced deposition. It was shown that deposition only occurred after the ilmenite sample was sufficiently reduced. For ilmenite oxidation, the mass change curves display a distinct peak followed by a valley when the sample was previously reduced in the presence of H 2 S, indicating reactions between the sulfur deposit and air. The amount of the sulfur deposit could be calculated using the oxidation curves. Scanning electron microscope-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) analyses were conducted to examine the surface of the reduced samples and the results from these analyses confirmed the presence of the sulfur deposit on the surface of the samples that were reduced in H 2 S-containing atmospheres.

Absorption processes for CO2 separation employing solid sorbents such as limestone appear to be t... more Absorption processes for CO2 separation employing solid sorbents such as limestone appear to be technically feasible and cost effective. At appropriate temperature and pressure, CO2 from flue gas stream is absorbed by CaO-based sorbent via the carbonation reaction, and the sorbent is then regenerated in a separate reactor and a nearly pure CO2 stream is produced suitable for industrial use or ultimate sequestration. This technology has now been demonstrated using the CANMET pilot-scale dual-fluidized bed system. Havelock limestone from eastern Canada, was used as the CO2 sorbent, while a synthesis gas mixture of air and CO2 (15％) was employed to represent combustion flue gas. Oxy-fuel combustion of biomass and coal was employed in the sorbent regenerating step, creating a high CO2 concentration off-gas stream suitable for sequestration. Pure O2 was mixed with recycled off-gas and this along with the excellent heat transfer characteristics of fluidized bed allowed us to use an O2 ratio of 40％ in the combustion gas. In addition, samples were characterized for pore distribution (nitrogen adsorption/desorption: BET and BJH) and skeleton characterization (density by He pycnometry), as well as changes in sample volume during hydration (sample swelling). The results obtained showed successful hydration even for hydration periods as short as 15 min, and very favorable sample properties. Their pore surface area, pore volume distribution and swelling during hydration are very promising with regard to their use in additional CO2 capture cycles or SO2 retention.

Powder Technology, Oct 1, 2020

International Journal of Greenhouse Gas Control, 2019

A great effort is still pending in terms of thorough bottom-up economic assessments in the partic... more A great effort is still pending in terms of thorough bottom-up economic assessments in the particular case of Chemical Looping Combustion (CLC) and Pressurized Chemical Looping Combustion (PCLC) processes. This work tries to reduce this knowledge gap through a comprehensive techno-economic analysis of PCLC technology focused on the replacement of a Once-through Steam Generator (OTSG) for the production of steam in a Steam Assisted Gravity Drainage (SAGD) facility in Alberta (Canada) by a PCLC system that burns natural gas using ilmenite as oxygen carrier. The evaluation of capital expenditure (CAPEX) for the different CLC cases analyzed revealed that the main contribution to costs stemmed from the rotating equipment. The economic performance of the CLC processes was evaluated through the Levelized Cost of Steam (LCOS) and the cost of CO 2 captured. These parameters ranged between 30.45 and 39.93 CAD/t of steam (23.61-30.95 USD/t) and between 44.39 and 107.05 CAD/t of CO 2 (34.41-82.98 USD/t), respectively. In the particular case of the CLC unit that operated at atmospheric pressure, the results were 34.92 CAD/t of steam (27.07 USD/t) and 75.46 CAD/t of CO 2 (58.50 USD/t), which highlighted the economic benefits resulting from the use of CLC technology under pressurized conditions. Finally, comparing the economic results obtained in this framework with those found in the literature using other Carbon Capture and Storage (CCS) technologies, it can be concluded that PCLC technology has the potential to be a competitive CO 2 capture option in the future for use in industrial SAGD facilities.

International Journal of Greenhouse Gas Control, 2018

International Journal of Greenhouse Gas Control, 2019

Chemical looping reforming is a promising option for the conversion of gaseous fuels to high qual... more Chemical looping reforming is a promising option for the conversion of gaseous fuels to high quality syngas suitable for gas-to-liquids (GtL) processes. This work evaluates the potential for syngas, heat, power, and steam generation for diluent production at steam assisted gravity drainage (SAGD) facilities using low cost ilmenite ore pressurized chemical looping reforming (PCLR). Preliminary fixed-bed reactor testing on a naturally occurring Canadian ilmenite ore was performed to determine the optimal operating regime for syngas generation. Based on SEM characterization, EDX elemental mapping, XRD, and Mössbauer spectroscopy measurements it was demonstrated that partial reduction to Fe 2.5+ and Fe 2+ containing species is required to avoid the production of CO 2. Additionally, the reduction to Fe°containing species should be minimized to limit the formation of carbon and metal carbides. These results were used to generate material and energy balances via Aspen HYSYS V9 process simulation software of the entire PCLR process for SAGD applications using a Canada's Oil Sands Innovation Alliance (COSIA) SAGD facility template. Thorough energy integration of the combined PCLR-SAGD process using Pinch Analysis suggests that steam and diluent requirements can be met, with excess power generation, at lower costs than more traditional syngas generation technologies, while meeting CO 2 emissions targets and reducing boiler feed water (BFW) make-up. Having shown that process performance is attractive, a techno-economic assessment to establish the most economical design for the PCLR-SAGD process is now required.

Energy technology, May 24, 2016

Chemical Engineering Journal

Fuel Processing Technology

The co-combustion of a high-sulphur lignite and biomass blend (up to 50% by weight) has been stud... more The co-combustion of a high-sulphur lignite and biomass blend (up to 50% by weight) has been studied in a small oxy-fired circulating fluidized bed combustion (CFBC) pilot plant. Here the goal is to examine the effect of biomass share on NO x , SO 2 and CO emissions. In these tests, a series of runs has looked at the effect of increasing biomass share under air firing, followed by tests in oxyfiring mode. The results show that the emissions are remarkably insensitive to the biomass share, and are comparable to other results for coal combustion, and likely to be well below any current emission guidelines. Overall, there appear to be no direct challenges to oxy-fuel co-firing in terms of gaseous emissions, although the simple lack of studies means that significantly more data are required on CFBC oxy-firing using a much wider range of biomass and coal types. K doping was also examined and did not result in significant formation of K phases on deposit probes.