Liquefaction Rate Research Articles

Reduction of real gas losses with a DC flow in the regenerator of the refrigeration cycle

Improving efficiency is an enduring effort for all refrigeration cycles. Real gases cause “intrinsic” heat losses in the regenerator and degrade the coefficient of performance (COP) of the regenerator of the refrigeration cycle. Previous experimental and numerical studies found that the COP of the regenerative refrigerator can be improved by imposing a direct-current (DC) flow, and the liquefaction rate can be improved by several times when the gas is precooled by the regenerator that works down to the temperatures close to or below the critical point. However, the working mechanism of such improvements has not been fully explored. In this paper, the working mechanism of imposing a DC flow on the regenerator working with a real gas is revealed based on thermodynamic analyses. The theoretical value of the DC flow and its influence on the COP of the regenerator are analyzed. The results show that the COP of the regenerator can be improved by over 10 times with a DC flow. An even higher relative Carnot COP of around 80% is possible to obtain in some specific temperature ranges. The enthalpy loss and the entropy loss of this approach has been estimated. This approach provides a potential way to improve the refrigeration COP and the liquefaction rate significantly. Measured liquefaction results found in the relevant literature have been analyzed to demonstrate the effectiveness of this approach.

Liquefaction of poplar biomass for value-added platform chemicals

This study shows that two groups of value-added platform chemicals, namely glucosides and phenolic compounds, can be obtained from the liquefaction of lignocellulosic biomass. The liquefaction of biomass was conducted in a methanol medium with H2SO4 as a catalyst at 120–220 °C. The effects of liquefaction temperature on the yield and distribution of the liquefied product and the change in liquefied residue were investigated. The maximum liquefaction rate was 91.13% at 220 °C based on the whole feedstock. The target products were glucosides and phenolic compounds, which were derived from the liquefaction of carbohydrates and lignin part in poplar biomass respectively, and could be effectively separated after liquefaction. The yields of glucosides and phenolic compounds reached 48.83 and 25.96% at 200 °C respectively. The glucosides mainly contained pentose and hexose glucosides with high a purity of 91.67% at 200 °C. The phenolic products were separated into four fractions with different molecular weight distributions. Overall, it achieved the simultaneous transformation of carbohydrates and lignin fractions in biomass into high value-added chemicals.

Plasma electrolytic liquefaction of cellulosic biomass

In this paper, the rapid liquefaction of a corncob was achieved by plasma electrolysis, providing a new method for cellulosic biomass liquefaction. The liquefaction rate of the corncob was 95% after 5 min with polyethylene glycol and glycerol as the liquefying agent. The experiments not only showed that H+ ions catalyzed the liquefaction of the corncob, but also that using accelerated H+ ions, which were accelerated by an electric field, could effectively improve the liquefaction efficiency. There was an obvious discharge phenomenon, in which the generated radicals efficiently heated the solution and liquefied the biomass, in the process of plasma electrolytic liquefaction. Finally, the optimum parameters of the corncob liquefaction were obtained by experimentation, and the liquefaction products were analyzed.

Experimental study on the liquefaction of cellulose in supercritical ethanol

Cellulose is the major composition of solid waste for producing biofuel; cellulose liquefaction is helpful for realizing biomass supercritical liquefaction process. This paper is taking supercritical ethanol as the medium, liquefied cellulose with the intermittence installation of high press cauldron. Experiments have studied technical condition and the technology parameter of cellulose liquefaction in supercritical ethanol, and the pyrolysis mechanism was analysed based on the pyrolysis product. Results show that cellulose can be liquefied, can get good effect through appropriate technology condition. Under not catalyst, highest liquefaction rate of cellulose can reach 73.5%. The composition of the pyrolysis product was determined by GC-MS.

Cascading pulse tubes on a large diaphragm pressure wave generator to increase liquefaction potential

Fabrum Solutions, in collaboration with Absolut System and Callaghan Innovation, produce a range of large pulse tube cryocoolers based on metal diaphragm pressure wave generator technology (DPWG). The largest cryocooler consists of three in-line pulse tubes working in parallel on a 1000 cm3 swept volume DPWG. It has demonstrated 1280 W of refrigeration at 77 K, from 24 kW of input power and was subsequently incorporated into a liquefaction plant to produce liquid nitrogen for an industrial customer. The pulse tubes on the large cryocooler each produced 426 W of refrigeration at 77 K. However, pulse tubes can produce more refrigeration with higher efficiency at higher temperatures. This paper presents the results from experiments to increase overall liquefaction throughput by operating one or more pulse tubes at a higher temperature to pre-cool the incoming gas. The experiments showed that the effective cooling increased to 1500 W resulting in an increase in liquefaction rate from 13 to 16 l/hour.

Thermodynamic analysis and economical evaluation of two 310-80 K pre-cooling stage configurations for helium refrigeration and liquefaction cycle

In 310-80 K pre-cooling stage, the temperature of the HP helium stream reduces to about 80 K where nearly 73% of the enthalpy drop from room temperature to 4.5 K occurs. Apart from the most common liquid nitrogen pre-cooling, another 310-80 K pre-cooling configuration with turbine is employed in some helium cryoplants. In this paper, thermodynamic and economical performance of these two kinds of 310-80 K pre-cooling stage configurations has been studied at different operating conditions taking discharge pressure, isentropic efficiency of turbines and liquefaction rate as independent parameters. The exergy efficiency, total UA of heat exchangers and operating cost of two configurations are computed. This work will provide a reference for choosing 310-80 K pre-cooling stage configuration during design.

Catalytic Liquefaction of Lignite by Supercritical Ethanol

Catalytic hydrogenation liquefaction by supercritical ethanol is an effective method for the efficient utilization of lignite. The liquefaction efficiencies of lignite 1(L1) and lignite 2(L2),which were collected from Zhaotong, Yunnan, were compared. It was found that the liquefaction efficiency of L1 was better than L2 but the gas yield of L2 was higher than L1 under the same reaction conditions, indicating that both of them could be effectively conversed. The yields of lipids and phenols in the components of liquefaction products were significantly different, and the liquefaction of L2 could achieve the desired conversion effect by changing the reaction conditions. Increasing the amount of ethanol could promote liquefaction efficiency, however, when the ratio of ethanol to coal(E/C) were 20 and 30, the growth rate of the yield of liquefied oil was quite lower than the previous stages. This phenomenon indicated that with the decrease of lignite concentration, the mass transfer effect of ethanol as a solvent in the reaction was getting better and better, and the liquefaction rate increased rapidly. But the higher system pressure was not conducive to liquefaction in high temperature conditions. In addition, the esterification reaction between ethanol and the intermediates of hydrocracking reaction could facilitate liquefaction reaction.

Synthetic natural gas (SNG) liquefaction processes with hydrogen separation

The fact that synthetic natural gas (SNG) contains hydrogen has a great impact on its liquefaction process. Aiming to produce liquefied natural gas (LNG) from SNG, hydrogen separation from SNG through cryogenic processes is studied. A new separation method combining distillation and flash is developed, resulting in higher liquefaction rate than that of distillation under same operating parameters. Process simulations are performed by combining one liquefaction part (a nitrogen expansion process or a mixed refrigerant one) and one distillation part (direct flash, atmospheric distillation, pressurized distillation or the new separation method). Compared to direct flash, distillation can reduce the hydrogen content of products to a very low level, increasing the temperature of products by 8 °C and reducing the unit power consumption by 3%; and, compared to the other three separation ways, the new separation method reduces the unit power consumption by 7–10%. Both nitrogen expansion and SMR liquefaction processes can be integrated with hydrogen separation, but power consumptions for SMR processes are less than those for nitrogen expansion ones.

43.太平洋炭の液化反応における水酸化銅の触媒効果(1) : 液化率に与える水酸化銅とその関連化合物の触媒効果

43.太平洋炭の液化反応における水酸化銅の触媒効果(1) : 液化率に与える水酸化銅とその関連化合物の触媒効果

Single and multiple objective optimization of a natural gas liquefaction process

Benefit from the development of process simulation technology, the optimal operating conditions of the natural gas liquefaction process can be obtained by simulation modeling and analysis. Based on the concept of the evolution theory, the genetic algorithm is an effective tool for the optimization of the liquefaction process. A single nitrogen expansion process with carbon dioxide pre-cooling is modeled in Aspen HYSYS, which is connected to MATLAB by ActiveX technology to establish a hybrid simulation platform. Taking the unit energy consumption and the liquefaction rate as the objective functions, the multi-objective optimization problem of the liquefaction process is constructed. The penalty function is employed to realize the conversion of the constraints. The simple and the fast elitist non-dominated sorting genetic algorithm are adopted to solve the single and multi-objective optimization problem of the liquefaction process, respectively. Results indicate that the simple genetic algorithm achieves low unit energy consumption and high heat transfer efficiency with the main objective method, while the results of the fast elitist non-dominated sorting genetic algorithm better realizes the synthetical performance of the process. The economic analysis shows that the initial investment is the key factor which restricts the economic performance of the project.

Development of helium refrigeration/ liquefaction system at BARC, India

An experimental helium refrigerator/liquefier, using ultra high speed cryogenic turboexpanders, is designed and developed at Cryo-Technology Division, BARC. The developed system is based on the modified Claude cycle. The developed system is presently fully functional consisting of process compressor with gas management system, coldbox, helium receiver Dewar, tri-axial transfer line and helium recovery system. Extended trial runs are conducted to evaluate the performance of the developed system. During these trials, liquefaction rate of around 32 l/hr and refrigeration capacity of around 190W is achieved. The paper addresses design, development and commissioning aspects of the developed helium liquefier along with results of performance evaluation trial runs.

The optimization on flow scheme of helium liquefier with genetic algorithm

There are several ways to organize the flow scheme of the helium liquefiers, such as arranging the expanders in parallel (reverse Brayton stage) or in series (modified Brayton stages). In this paper, the inlet mass flow and temperatures of expanders in Collins cycle are optimized using genetic algorithm (GA). Results show that maximum liquefaction rate can be obtained when the system is working at the optimal parameters. However, the reliability of the system is not well due to high wheel speed of the first turbine. Study shows that the scheme in which expanders are arranged in series with heat exchangers between them has higher operation reliability but lower plant efficiency when working at the same situation. Considering both liquefaction rate and system stability, another flow scheme is put forward hoping to solve the dilemma. The three configurations are compared from different aspects, they are respectively economic cost, heat exchanger size, system reliability and exergy efficiency. In addition, the effect of heat capacity ratio on heat transfer efficiency is discussed. A conclusion of choosing liquefier configuration is given in the end, which is meaningful for the optimal design of helium liquefier.

Factors Influencing Polyol Liquefaction of Nut Shells of Different Camellia Species

The liquefaction rates and kinetics of nut shells of different Camellia species in PEG400/glycerol/H2SO4 liquefying solvent were investigated. Changes in major components including cellulose, hemicellulose, and lignin as well as cellulose crystallinity of the nut shells were determined. The compositions of the liquefaction residues were analyzed. Results indicated that, under the same conditions, the liquefaction rates of nut shells of different Camellia species were noticeably different and the PEG400/glycerol/H2SO4 liquefaction agent was not suitable for the liquefaction of the nut shells of all Camellia species. The burst liquefaction of Camellia nut shells (CNSs) that occurred during the first stage was due to the rapid degradation of hemicellulose, acid-soluble lignin, and amorphous cellulose. The liquefaction during the second stage became very slow, mostly because the swelling and decomposition of crystalline cellulose was very difficult to achieve with the liquefying agent and the liquefaction products inhibited liquefaction at later stages. The liquefaction residues of CNSs were composed of crystalline cellulose, small amounts of hemicellulose, acid-insoluble lignin, and ash. Ash was partially dissolved in the liquefying agent. The liquefaction rates of all CNSs tested in this study showed linear relationships with time, with coefficients of determination (R2) greater than 0.7082, indicating that the liquefaction of CNS was a pseudo-first-order reaction.

Non-invasive thrombolysis using microtripsy for deep vein thrombosis and intracerebral hemorrhage

Histotripsy has been demonstrated as a non-invasive, drug-free, image-guided thrombolysis method using cavitation alone. Microtripsy is a new histotripsy approach, where cavitation is generated using 1-cycle ultrasound pulses with negative pressure exceeding a threshold intrinsic to the medium. We investigated microtripsy for treatment of deep vein thrombosis (DVT) and intracerebral hemorrhage (ICH). First, the in vivo feasibility of using microtripsy to treat DVT was investigated. Guided by ultrasound imaging, microtripsy thrombolysis treatment was applied to the clot formed in the femoral vein in 14 pigs using 1 μs-long pulses at a pulse repetition frequency of 100 Hz and a peak negative pressure of 30 MPa by a 1 MHz transducer. Blood flow was restored or significantly increased in 13 out of the 14 pigs confirmed by color Doppler. Minor hemolysis was observed. No vessel damage was observed on histology. Second, microtripsy was investigated to liquefy and drain clots through excised human skulls for ICH treatment using a 256-element, 500 kHz phased array transducer. Microtripsy generated individual lesions of 0.1 to 1.5 mm at the geometric location and electronically steered positions out to 20 mm from the geometric focus. By electronically steering the focus to cover a clot volume, microtripsy liquefied 40 mL of clot in 25 min, resulting in clot liquefaction rate of 1.6 mL/min.

Proposal and design of a natural gas liquefaction process recovering the energy obtained from the pressure reducing stations of high-pressure pipelines

Taking advantage of the refrigerating effect in the expansion at an appropriate temperature, a fraction of high-pressure natural gas transported by pipelines could be liquefied in a city gate station through a well-organized pressure reducing process without consuming any extra energy. The authors proposed such a new process, which mainly consists of a turbo-expander driven booster, throttle valves, multi-stream heat exchangers and separators, to yield liquefied natural gas (LNG) and liquid light hydrocarbons (LLHs) utilizing the high-pressure of the pipelines. Based on the assessment of the effects of several key parameters on the system performance by a steady-state simulation in Aspen HYSYS, an optimal design condition of the proposed process was determined. The results showed that the new process is more appropriate to be applied in a pressure reducing station (PRS) for the pipelines with higher pressure. For the feed gas at the pressure of 10MPa, the maximum total liquefaction rate (ytot) of 15.4% and the maximum exergy utilizing rate (EUR) of 21.7% could be reached at the optimal condition. The present process could be used as a small-scale natural gas liquefying and peak-shaving plant at a city gate station.

Hydrocracking of Organosolv Lignin in Subcritical Water to Useful Phenols Employing Various Raney Nickel Catalysts

Hydrothermal conversion of organosolv lignin has been conducted under a reductive hydrogen atmosphere near the critical point of water. Several Raney nickel catalysts were tested with respect to degree of liquefaction, yields of phenols, and influence on the product distribution. The application of Raney nickel catalysts is crucial for the hydrothermal liquefaction of lignin since the liquefaction rate increased approximately 2.5 times compared to hydrothermal conversion without catalysts. In addition, Raney nickel caused complete demethoxylation of guaiacyl and syringyl moieties resulting in an oil composed mainly of six highly reactive simple phenols (phenol and monoalkylated derivatives). Depending on the catalyst type, yields of these phenols were 1.3–8.0 wt % (≈2.6%–16% theoretical yield). Flash pressure release with subsequent condensation of the hot vapors proved to be a fast and easy approach to obtain a liquid fraction with a high content (25%) of phenol and para- or ortho-alkylated derivatives, ...

Commissioning Test Results of Variable-Temperature Helium Refrigerator/Liquefier for NIFS Superconducting Magnet Test Facility

The superconducting magnet test facility in the National Institute for Fusion Science has been upgraded for excitation tests at a wide temperature range and a higher magnetic field of 13 T. As part of the upgrade, the helium refrigerator/liquefier that operated for 24 years was replaced with a variable-temperature helium refrigerator/liquefier. The required liquefaction rate is 250 L/h, and the required refrigeration capacity is 600 W at 4.5 K, same as the previous one. In addition, it has a new feature that can supply helium gas of a wide temperature range. The typical design cooling capacity is 1 kW under the condition of 20-K supply/30-K return and 1.5 kW under the condition of 40-K supply/50-K return. After the replacement, a series of commissioning tests were performed under the various operational conditions. From the results, the satisfactory thermodynamic performance was confirmed. In the future, it is expected that the substantial progress will be made in the development of large-scale superconducting magnets with advanced superconductors such as high-temperature superconductors and MgB2. The design of the variable-temperature helium refrigerator/liquefier and the results of the commissioning tests are reported in detail.

Large >60 gallon/day ‘pulse-tube’ oxygen liquefier for aircraft carriers

An oxygen liquefier using a large ‘pulse-tube’ or acoustic-Stirling cryocooler is described, which has a liquefaction rate in excess of 60 gallons per day (227 liters per day) as measured by the increase in weight of a storage dewar, from <20 kWe input. Several of these systems will be deployed on U.S. Navy aircraft carriers to provide shipboard liquid oxygen. Paths to improvement in future systems are identified, although it is noted that since the present system exceeds the required specifications, these improvements may not be implemented in the near term.

Optimisation of expansion liquefaction processes using mixed refrigerant N2–CH4

An expansion process with a pre-cooling system is simulated and optimised by Aspen HYSYS and MATLAB™. Taking advantage of higher specific refrigeration effect of methane and easily reduced refrigeration temperature of nitrogen, the designed process adopts N2–CH4 as a mixed refrigerant. Based on the different thermodynamic properties and sensitivity difference of N2 and CH4 over the same heat transfer temperature range, this work proposes a novel method of matching refrigerant composition which aims at single-stage or multi-stage series expansion liquefaction processes with pre-cooling systems. This novel method is applied successfully in propane pre-cooled N2–CH4 expansion process, and the unit power consumption is reduced to 7.09 kWh/kmol, which is only 5.35% higher than the global optimised solutions obtained by genetic algorithm. This novel method can fulfil the accomplishments of low energy consumption and high liquefaction rate, and thus decreases the gap between the mixed refrigerant and expansion processes in energy consumption. Furthermore, the high exergy efficiency of the process indicates good adaptability to varying natural gas compositions.

Wood liquefaction with phenol by microwave heating and FTIR evaluation

We examined wood liquefaction using phenol and mixed acid catalysts with microwave heating, and compared that with similar processes that use oil bath heating. The reaction time for microwave heating to achieve a residue content was one sixth, one eighteenth, and one twenty-fourth of that from oil bath heating, respectively, for phenol to wood (P/W) ratios of 2.5/1, 2/1 and 1.5/1. A low P/W ratio tended to result in carbonization of liquefied wood due to an insufficient amount of phenol and localized microwave superheating. Fourier transform infrared spectroscopic (FTIR) evaluation of the liquefied residue, showed that the liquefaction rates of wood components differed. Hemicellulose was most susceptible to liquefaction, crystalline cellulose was most recalcitrant, and guaiacyl units the most prone to re-condensation. From FTIR, the chemical components and substitution patterns of bonded phenol were similar for both methods.