Backpressure Mode Research Articles

Feasibilities of utilizing thermal inertia of district heating networks to improve system flexibility

The use of district heating network inertia (DHNI) has been regarded as an efficient and cost-saving method to improve the flexibility of the energy systems. However, the acclaimed benefits in most studies are found in specific cases with traditional middle-temperature systems. The cases where DHNI is not feasible are unclear and the applicability of DHNI in future low-temperature district heating (LTDH) systems requires further investigations. Therefore, this study applied a top-down methodology where the practical storage potentials of DH networks are evaluated based on field investigations of 134 Swedish DH networks and 25 Chinese DH networks with various sizes and demand densities. Empirical relationships between the heat density and storage potentials are established and analyzed. Then, bottom-level analysis from technical and economical aspects are conducted on a variety of application scenarios for DHNI, including different temperature levels, heat sources, control strategies and renewable energy profiles. It is found that in LTDH system, by raising the network temperatures to actively use the DHNI, the heat source efficiency is reduced regardless the size and density of the network and, thereby, making the DHNI infeasible. This implies that the DHNI is only applicable in middle-temperature systems with combined heat and power plant (CHP) as a heat source in the extraction mode. Furthermore, the back-pressure mode is not economically attractive. In summary, the results from a multi-scenario analysis identified limited benefits of the DHNI, implying a proper consideration of its roles in future works.

Development of the composition and production technology of injection medication for intra-articular introduction based on sodiun hyaluronate

Osteoarthrosis is the most widespread disease of musculoskeletal system, which leads to different level of disability in 10–30% of cases. The age of the person is one of the key risk factors for the development of such disease. The most effective resolution is a surgery in which joints are replaced, but this method is very risky and expensive especially for elderly people. That is why development of the composition and research in new technological aspects of biotechnological medication is an actual course in pharmacy.
 The aim of research: development of the composition and production technology of injection solution of hyaluronic acid as sodium hyaluronate for the therapy of degenerate inflammatory disease of articulation.
 The object of the study is an injection with sodium hyaluronate for intra-articular administration.
 Evaluation of the test results when choosing the optimal technology for preparing the injection solution was carried out by the visual method (description, transparency), and by the method of rotational viscometry (viscosity). The suitability of the sterilization regime was determined by physicochemical methods (appearance, transparency, viscosity, pH of the solution) and microbiological method (sterility) according to the requirements of SPhU. The quantitative content of sodium hyaluronate was determined by spectrophotometry (SPhU, 2.2.25) using a carbazole reagent.
 The results of the studies has been developed the optimal composition of the drug based on stabilized sodium hyaluronate by the excipient BDE. The resulting solution in its physical-chemical properties are a clear, highly viscous aqueous solution. The developed composition contains (in %): Sodium hyaluronate with a molecular weight of ~ 2 MDA (in terms of 100% substance) – 1.0; BDE – 0.75; sodium chloride – 0.85; phosphate buffer – up to pH from 5.0 to 8.5; water for injection – up to 100%.
 The critical parameters of the technological stages for the production of a drug with sodium hyaluronate are determined experimentally. Specific critical parameters are the degassing of a viscous solution, filtration and the conditions of the sterilization mode of the injection solution. It was experimentally established that the optimal parameters for the filtration stage are the use of a Durapore hydrophilic membrane made of polyvinyl difluoride (PVDF), the temperature of the solution is 50 ± 0.5 °C and the use of back pressure mode to reduce the volume wich is filtered per unit time. It was determined that the sterilization mode with saturated steam at a temperature of 121 °C for 8 min is optimal and ensures the quality of the solution in quality criterion of «Sterility».
 Samples of the experimental series of injection solution, obtained by the developed technology, comply with the requirements of SPhU for drugs for parenteral use according to physical-chemical and biological quality criteria as appearance, transparency, viscosity, pH of the solution, sterility, assay sodium hyaluronate.

Multi-objective combined heat and power unit commitment using particle swarm optimization

The unit commitment (UC) problem is formulated by undertaking dual operating mode combined heat and power (CHP) units along with thermal and heat units. The extraction and backpressure mode of the CHP unit provides the facility to adopt immediate change in the generation, which depends upon the ratio of the heat and power generation. The impact of dual-mode CHP (DM-CHP) unit has been examined on multi-objective (MO) economic and profit based models, in order to deal with pollutant emission along with cost/profit. The model of CHP-UC problem is a mixed integer model, hence to deal with binary and real variables, binary particle swarm optimization (BPSO) and PSO technique have been employed, respectively. To demonstrate the effectiveness of the optimization technique, two test systems of thermal UC problem have been undertaken and the results are compared. In order to verify the benefits of DM-CHP unit, three test systems of CHP-UC problem have been undertaken and the impact of backpressure and extraction mode of CHP unit has been investigated in terms of cost/profit and emission. It has been verified from the results that backpressure and extraction mode of the CHP unit provide diverse UC status and generation schedule.

Performance analysis and optimization of a NGCC-CHP plant with low pressure economizer partial recirculation system

In this paper, the performance of a natural gas combined cycle (NGCC) power plant operating in combined heat and power (CHP) mode is analyzed, and the optimization of partial recirculation system is conducted. In order to compare the plant performances between complete and partial recirculation systems, the simulations of NGCC-CHP plants with both systems are performed. Base on the off-design characteristics of both systems, the optimal operating strategies are proposed to achieve energy utilization efficiency. The comparisons on thermodynamic performance and operational flexibility between the plants with both systems are performed. Results show that in contrast with the complete recirculation system, the partial recirculation system can improve the energy utilization efficiency of the NGCC-CHP plant by 0.48–0.58% at various conditions. More waste heat can be recovered from flue gas under the limitation of dew point corrosion. Moreover, the heat generation capacity of the plant increases and the operational gap between extraction-condensing mode and backpressure mode of the plant shrinks. The plant achieves the decoupling between power generation and heat generation at backpressure mode. The combined heat and power operational continuity and flexibility of the plant with partial recirculation system is superior to that with complete recirculation system.

Unit commitment considering dual-mode combined heat and power generating units using integrated optimization technique

In this work, we have undertaken a dual-mode combined heat and power unit commitment model to address the optimum generation scheduling of the committed unit. The model formulation includes the backpressure and an extraction mode of cogeneration unit, which is having a diverse feasible operating region of operation. In backpressure mode, the energy generated from the combined heat and power unit depends on a fixed ratio of power and heat, while in extraction mode, this ratio is relatively relaxed that provides system flexibility as compared to other. Owing to the dynamic features of different generating units as well as combination of binary and continuous decision variables, the problem becomes mixed-integer nondeterministic polynomialhard optimization problem, hence an integrated optimization technique has been applied. The integrated optimization technique is a combination of binary successive approximation technique and civilized swarm optimization technique. The binary successive approximation as a local search technique is used to update the unit status, iteratively and global search technique ‘civilized swarm optimization’ are applied to search optimal generation schedule from the committed units. In order to measure the impact of a dual-mode combined heat and power unit on optimum generation scheduling and system flexibility, four test systems have been undertaken. It has been observed from results that total operating cost of the system during extraction mode of combined heat and power unit is less as compared to backpressure mode. It is also evident from the results, that system provides diverse flexibility in terms of power and heat capability, during the extraction and backpressure mode of operation.

Metal flow controlled by back pressure in the forming process of rib-web parts

In the forming process of rib-web parts, which are widely used in automobiles and aircrafts, severe streamline disorder often occurs because of unreasonable metal flow. In this study, a back-pressure-controlled forming method that can control the direction of metal flow was introduced. The effects of key parameters on metal flow were investigated, including the back-pressure value, loading mode, and back-pressure distance. The results showed that streamline defects can be avoided and the final forming load can be reduced by reasonably controlling the back-pressure parameters. The constant back-pressure mode was more conducive to achieving good forming quality compared with the linear-increased back-pressure mode. From the stress analysis of metal flow, it was demonstrated that the stress state in the rib root is changed by the back pressure, which makes the metal flow more easily along either the tangential or the radial direction. The advantages of the back-pressure-controlled forming method were confirmed by applying it to a compressor scroll rotor.

Heat Recovery Aspects of Importance for the Product Mix and GHG Emission Reductions in a Bio-SNG System

This paper presents the impact of adjusted operating parameters (superheating temperature and backpressure or condensing mode) for the heat recovery steam cycle (HRSC) by external conditions on the product mix (SNG; power and heat) in a commercial scale gasification-based bio-SNG (biomass derived synthetic natural gas) production system. The GHG reduction potentials for a case with a condensing HRSC and for a case with the HRSC in backpressure mode producing heat for CO2 separation of the flue gases are evaluated. Pinch technology was used to identify the potential for heat recovery and process integration. Small changes in the operational parameters of the HRSC can result in significant changes of the conversion efficiencies of heat and power. With an HRSC in back-pressure mode, reducing the power production by 4 MW compared to the condensing case, it is possible to produce ~60 MW of heat for district heating. This study shows that approximately one third of the carbon input to the gasifier ends up in the SNG, whereas one third is separated prior to methanation and one third is emitted as CO2 in the flue gases from the combustor of the indirect gasifier. If infrastructure for CO2 storage is available, and CO2 separated from the process and from the flue gases is stored, the GHG emission reductions from the bio-SNG system can be doubled compared to a case without CO2 storage possibility.

출력포트 확장 방식을 사용한 입출력 버퍼형 ATM 교환기에서의 성능 비교 분석

입력과 출력에 버퍼를 갖는 ATM 교환기의 셀 폐기 방법은 기존의 귀환(Backpressure)모드와 손실(Queueloss)모드가 있으며, 최근에는 두 모드의 단점을 보완한 하이브리드(Hybrid)모드가 제안되었다. 하이브리드모드는 목적하는 출력 버퍼와 입력 버퍼가 모두 포화일 경우에만 셀을 폐기하는 방식이다. 본 논문에서는 유니폼 트래픽하에서 Output-port expansion 기법을 사용한 귀환 손실 모드 및 하이브리드모드 하에서의 셀 손실률과 셀 지연을 성능 비교 분석한다 Output-port expansion 기법은, 한 타임 슬롯동안에 입력포트 당 하나의 셀만 교환되며, 만약 하나 이상의 셀들이 같은 출력포트로 향하고자 하면, 최대 교환되는 셀 수를 K(Output-port expansion ratio)개로 제한하는 방식이다. 셀 손실률을 비교 분석한 결과, 이전의 연구에서와는 달리 로드 0.9를 기점으로. 0.9이하의 로드에서는 하이브리드 모드가, 0.9 이상의 로드에서는 손실모드가 가장 낮은 셀 손실률을 보인다. 셀 지연을 비교 분석한 결과, 한 개의 교환기 성능 분석에서는 셀 손실로 인한 재전송(retransmission)을 고려하지 않는 관계로, 예상한 바와 같이, 로드가 많아질수록 셀 손실률이 높은 귀환모드가 K를 높일수록 다른 모드에 비해 낮은 셀 지연을 보였다. An input and output buffering ATM switch conventionally operates in either Queueloss mode or Backpressure mode. Recently, a new mode, which is called Hybrid mode, was proposed to overcome the drawbacks of Queueloss mode and Backpressure mode. In Hybrid mode, when both the destined output buffer and the originfted input buffer are full, a cell is dropped. This thesis analyzes the cell loss rate and the cell delay of Queueloss, Backpressure and Hybrid modes in a switch adopting output-port expansion scheme under uniform traffic. Output-port expansion scheme allows only one cell from an input buffer to be switched during one time slot. If several cells switch to a same destined output port, the number of maximum transfer cells is restricted to K (Output-port expansion ratio). The simulation results show that if an offered load is less than 0.9, Hybrid mode has lower cell loss rate than the other modes; otherwise, Queueloss mode illustrates the lowest cell loss rate, which is a different result from previous researches. However, the difference between Hybrid and Queueloss modes is comparably small. As expected, the average cell delay in Backpressure mode is lower than those of Queueloss mode and Hybrid mode, since the cell delay due to the retransmission of higher number of dropped cells in Backpressure mode is not considered.

Input and output queueing ATM switch with backpressure mode and queue loss mode for nonuniform traffic

An input and output queueing ATM switch model with a backpressure (BP) mode and a queue loss (QL) mode to decrease the system delay and the cell loss probability under nonuniform traffic is proposed. In the proposed model, the QL mode is adopted if the size of the backpressure exceeds the threshold. We consider a synchronous system with Bernoulli arrivals under hot-spot traffic that consists of a single output port of higher access rate superimposed on a background uniform traffic. The system delay and cell loss probability are analyzed under hot-spot traffic. It is shown that the proposed model is useful for nonuniform traffic. We also evaluate the effects of the threshold of the backpressure size for adopting the QL mode on the performance, and consider the optimum value of the threshold. © 1998 Scripta Technica, Electron Comm Jpn Pt 1, 81(11): 14–23, 1998

Analysis of input and output queueing for nonblocking ATM switches

A switch model for ATM networks is analyzed. Its interconnection network is internally nonblocking and is provided with dedicated input and output queues, one per switch inlet and one per switch outlet. The switch operates with an internal speed-up: more than one packet per slot can be transferred from the head-of-line positions of the input queues to each output queue by the interconnection network. Two different operation modes are considered for the interaction between input and output queues: backpressure mode and queue loss mode. The analytical model developed for the evaluation of the switch performance under random traffic assumes an infinite size for the switch, arbitrary values for input and output queue size, as well as for the speed-up factor. Switch throughput, packet delay and loss performance are evaluated and the analytical model accuracy is assessed using computer simulation results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>