Comparing Non-Steady State Emissions under Start-Up and Shut-Down Operating Conditions with Steady State Emissions for Several Industrial Sectors: A Literature Review

Combined Cycle Power Plants (CCPP) are attractive electricity generation systems due to high cycle efficiency and quick response of the system to load change. Heat recovery steam generator (HRSG) is an important part of a CCPP and it is important to predict the HRSG operating conditions in transient and steady state modes. It should be emphasized that the biggest pressure and thermal stresses are imposed on HRSG superheater and evaporator tubes banks during transient periods (cold start up and load change). Due to these effects a software program was developed for analyzing the HRSG transient and steady state operating conditions. The HRSG software included arbitrary number of pressure levels (usually up to three) and any number of elements (superheater, evaporator, economizer, desuperheater and duct burner). In this paper theories and equations (mass/energy balance and heat transfer coefficients) applied for HRSG thermal analysis are described. Also HRSG program software outputs were compared with real data collected from HRSG cold start-up at Tehran CCPP with specified geometry and arrangement of elements. The closeness of two groups of data in this transient and steady state modes was acceptable. The numerical outputs in steady state condition also were found very close to GT MASTER program software outputs.

Download Full-text

Experience with UASB reactor start-up under different operating conditions

Water Science & Technology ◽

10.2166/wst.1996.0578 ◽

1996 ◽

Vol 34 (5-6) ◽

pp. 421-428 ◽

Cited By ~ 41

Author(s):

M. M. Ghangrekar ◽

S. R. Asolekar ◽

K. R. Ranganathan ◽

S. G. Joshi

Keyword(s):

Steady State ◽

Operating Conditions ◽

Cod Removal ◽

Upflow Anaerobic Sludge Blanket ◽

Anaerobic Sludge ◽

Operating Parameters ◽

Reactor Performance ◽

Loading Rates ◽

Start Up ◽

Sludge Production

Four laboratory upflow anaerobic sludge blanket (UASB) reactors were operated at different operating parameters viz., hydraulic retention time (HRT), upflow velocity, organic concentration, and Ca2+ concentration in the wastewater. These operating parameters gave different values of organic loading rates (OLRs) and sludge loading rates (SLRs). The reactor performance during start-up was evaluated at different values of the above listed parameters. Also, the effects of these parameters on the granule characteristics were investigated. It was observed that COD removal efficiency at steady state was profoundly influenced by SLR. The reactor started with SLR of 0.6 kgCOD/ kg VSS.d could result in about 50% COD removal at steady state. The reactor performance could not improve even after three months of operation. Up to 0.3 kgCOD/ kgVSS.d the reactor performance was good with more than 90% COD removal at steady state. The OLD and SLR also determine time required for the reactor to achieve steady state. Different operating conditions also have the bearing on the strength of the granules cultivated. The methanogenic activity measured on acetate for each reactor was observed between 0.259 and 0.909 kg CH4 COD/ kgVSS.d. The sludge production in all the reactors was between 0.087 and 0.13 kgVSS/ kgCODin. The mathematical model was developed in order to predict sludge production.

Download Full-text

Microbial Community Successional Changes in a Full-Scale Mesophilic Anaerobic Digester from the Start-Up to the Steady-State Conditions

Microorganisms ◽

10.3390/microorganisms9122581 ◽

2021 ◽

Vol 9 (12) ◽

pp. 2581

Author(s):

Barbara Tonanzi ◽

Simona Crognale ◽

Andrea Gianico ◽

Stefano Della Sala ◽

Paola Miana ◽

...

Keyword(s):

Steady State ◽

Activated Sludge ◽

Biogas Production ◽

16S Rrna Gene Sequencing ◽

Full Scale ◽

Operating Conditions ◽

Rrna Gene ◽

Sludge Stabilization ◽

Start Up ◽

Fermentative Bacteria

Anaerobic digestion is a widely used technology for sewage sludge stabilization and biogas production. Although the structure and composition of the microbial communities responsible for the process in full-scale anaerobic digesters have been investigated, little is known about the microbial successional dynamics during the start-up phase and the response to variations occurring in such systems under real operating conditions. In this study, bacterial and archaeal population dynamics of a full-scale mesophilic digester treating activated sludge were investigated for the first time from the start-up, performed without adding external inoculum, to steady-state operation. High-throughput 16S rRNA gene sequencing was used to describe the microbiome evolution. The large majority of the reads were affiliated to fermentative bacteria. Bacteroidetes increased over time, reaching 22% of the total sequences. Furthermore, Methanosaeta represented the most abundant methanogenic component. The specific quantitative data generated by real-time PCR indicated an enrichment of bacteria and methanogens once the steady state was reached. The analysis allowed evaluation of the microbial components more susceptible to the shift from aerobic to anaerobic conditions and estimation of the microbial components growing or declining in the system. Additionally, activated sludge was investigated to evaluate the microbial core selected by the WWTP operative conditions.

Download Full-text

Validation of On-line Respiration Meter and its Applications by Computer Simulation

Water Science & Technology ◽

10.2166/wst.1992.0578 ◽

1992 ◽

Vol 26 (5-6) ◽

pp. 1355-1363 ◽

Cited By ~ 2

Author(s):

C-W. Kim ◽

H. Spanjers ◽

A. Klapwijk

Keyword(s):

Steady State ◽

Activated Sludge ◽

Respiration Rate ◽

Oxygen Demand ◽

Operating Conditions ◽

Mass Balances ◽

Short Term ◽

Respiration Rates ◽

On Line ◽

Made In

An on-line respiration meter is presented to monitor three types of respiration rates of activated sludge and to calculate effluent and influent short term biochemical oxygen demand (BODst) in the continuous activated sludge process. This work is to verify if the calculated BODst is reliable and the assumptions made in the course of developing the proposed procedure were acceptable. A mathematical model and a dynamic simulation program are written for an activated sludge model plant along with the respiration meter based on mass balances of BODst and DO. The simulation results show that the three types of respiration rate reach steady state within 15 minutes under reasonable operating conditions. As long as the respiration rate reaches steady state the proposed procedure calculates the respiration rate that is equal to the simulated. Under constant and dynamic BODst loading, the proposed procedure is capable of calculating the effluent and influent BODst with reasonable accuracy.

Download Full-text

Cake Formation in Cross-Flow Microfiltration Systems

Water Science & Technology ◽

10.2166/wst.1992.0244 ◽

1992 ◽

Vol 25 (10) ◽

pp. 149-162 ◽

Cited By ~ 20

Author(s):

V. L. Pillay ◽

C. A. Buckley

Keyword(s):

Cross Flow ◽

Operating Conditions ◽

Waste Waters ◽

Domestic Waste ◽

Time Curve ◽

Good Correspondence ◽

Operating Variables ◽

Start Up ◽

Turbulent Flow Regime ◽

Cake Formation

Cross-flow microfiltration (CFMF) has potentially wide application in the processing of industrial and domestic waste waters. Optimum design and operation of CFMF systems necessitates a knowledge of the characteristic system behaviour, and an understanding of the mechanisms governing this behaviour. This paper is a contribution towards the elucidation and understanding of the behaviour of a woven fibre CFMF operated in the turbulent flow regime. The characteristic flux-time curve and effects of operating variables on flux are presented for a limestone suspension cross-flow filtered in a 25 mm woven fibre tube. The phenomena contributing to the shape of the flux-time curve are discussed. A model of the mechanisms governing cake growth and limit is presented. Predicted steady-state fluxes show a notably good correspondence with experimentally measured values. It is also found that the flux may not be uniquely defined by the operating conditions, but may also be a function of the operating path taken to reach the operating point. This is of significance in the start-up and operation of CFMF units.

Download Full-text

Steady-state Security Assessment Based on K-Means Clustering Algorithm and Phasor Measurement Units

Recent Advances in Electrical & Electronic Engineering (Formerly Recent Patents on Electrical & Electronic Engineering) ◽

10.2174/1874476105666190830112118 ◽

2020 ◽

Vol 13 (4) ◽

pp. 559-570

Author(s):

Bassam A. Hemade ◽

Hamed A. Ibrahim ◽

Hossam E.A. Talaat

Keyword(s):

Steady State ◽

Clustering Algorithm ◽

System Security ◽

Phasor Measurement Units ◽

Operating Conditions ◽

Security Assessment ◽

State Security ◽

Phasor Measurement ◽

Measurement Units ◽

Silhouette Analysis

Background: The security assessment plays a crucial role in the operation of the modern interconnected power system network. Methods: Hence, this paper addresses the application of k-means clustering algorithm equipped with Principal Component Analysis (PCA) and silhouette analysis for the classification of system security states. The proposed technique works on three principal axes; the first stage involves contingency quantification based on developed insecurity indices, the second stage includes dataset preparation to enhance the overall performance of the proposed method using PCA and silhouette analysis, and finally the application of the clustering algorithm over data. Results: The proposed composite insecurity index uses available synchronized measurements from Phasor Measurement Units (PMUs) to assess the development of cascading outages. Considering different operational scenarios and multiple levels of contingencies (up to N-3), Fast Decoupled Power Flow (FDPF) have been used for contingency replications. The developed technique applied to IEEE 14-bus and 57-bus standard test system for steady-state security evaluation. Conclusion: The obtained results ensure the robustness and effectiveness of the established procedure in the assessment of the system security irrespective of the network size or operating conditions.

Download Full-text

Mathematical modelling of salt purification by recrystallization. Countercurrent arrangement

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19862481 ◽

1986 ◽

Vol 51 (11) ◽

pp. 2481-2488

Author(s):

Benitto Mayrhofer ◽

Jana Mayrhoferová ◽

Lubomír Neužil ◽

Jaroslav Nývlt

Keyword(s):

Steady State ◽

Simple Model ◽

Mathematical Modelling ◽

Distribution Coefficient ◽

Mother Liquor ◽

Equilibrium Temperature ◽

Operating Conditions ◽

Limiting Case

The paper presents a simple model of recrystallization with countercurrent flows of the solution and the crystals being purified. The model assumes steady-state operating conditions, an equilibrium between the outlet streams of each stage, and the same equilibrium temperature and distribution coefficient for all stages. With these assumptions, the model provides the basis for analyzing the variation in the degree of purity as a function of the number of recrystallization stages. The analysis is facilitated by the use of a diagram constructed for the limiting case of perfect removal of the mother liquor from the crystals between the stages.

Download Full-text

Applications of Biocatalysts for Sustainable Oxidation of Phenolic Pollutants: A Review

Sustainability ◽

10.3390/su13158620 ◽

2021 ◽

Vol 13 (15) ◽

pp. 8620

Author(s):

Sanaz Salehi ◽

Kourosh Abdollahi ◽

Reza Panahi ◽

Nejat Rahmanian ◽

Mozaffar Shakeri ◽

...

Keyword(s):

Phenolic Compounds ◽

Operating Conditions ◽

Phenolic Pollutants ◽

Petroleum Refinery Wastewater ◽

Start Up ◽

Low Concentrations ◽

Effective Removal ◽

Wide Range ◽

Loading Effects ◽

Spent Caustic

Phenol and its derivatives are hazardous, teratogenic and mutagenic, and have gained significant attention in recent years due to their high toxicity even at low concentrations. Phenolic compounds appear in petroleum refinery wastewater from several sources, such as the neutralized spent caustic waste streams, the tank water drain, the desalter effluent and the production unit. Therefore, effective treatments of such wastewaters are crucial. Conventional techniques used to treat these wastewaters pose several drawbacks, such as incomplete or low efficient removal of phenols. Recently, biocatalysts have attracted much attention for the sustainable and effective removal of toxic chemicals like phenols from wastewaters. The advantages of biocatalytic processes over the conventional treatment methods are their ability to operate over a wide range of operating conditions, low consumption of oxidants, simpler process control, and no delays or shock loading effects associated with the start-up/shutdown of the plant. Among different biocatalysts, oxidoreductases (i.e., tyrosinase, laccase and horseradish peroxidase) are known as green catalysts with massive potentialities to sustainably tackle phenolic contaminants of high concerns. Such enzymes mainly catalyze the o-hydroxylation of a broad spectrum of environmentally related contaminants into their corresponding o-diphenols. This review covers the latest advancement regarding the exploitation of these enzymes for sustainable oxidation of phenolic compounds in wastewater, and suggests a way forward.

Download Full-text

Personality trait differences across types of entrepreneurs: a systematic literature review

Review of Managerial Science ◽

10.1007/s11846-021-00466-9 ◽

2021 ◽

Author(s):

Florentine U. Salmony ◽

Dominik K. Kanbach

Keyword(s):

Literature Review ◽

Personality Traits ◽

Systematic Literature Review ◽

Empirical Studies ◽

Academic Research ◽

Future Research ◽

Rural Farmers ◽

Start Up ◽

Wide Range ◽

Research Integration

AbstractThe personality traits that define entrepreneurs have been of significant interest to academic research for several decades. However, previous studies have used vastly different definitions of the term “entrepreneur”, meaning their subjects have ranged from rural farmers to tech-industry start-up founders. Consequently, most research has investigated disparate sub-types of entrepreneurs, which may not allow for inferences to be made regarding the general entrepreneurial population. Despite this, studies have frequently extrapolated results from narrow sub-types to entrepreneurs in general. This variation in entrepreneur samples reduces the comparability of empirical studies and calls into question the reviews that pool results without systematic differentiation between sub-types. The present study offers a novel account by differentiating between the definitions of “entrepreneur” used in studies on entrepreneurs’ personality traits. We conduct a systematic literature review across 95 studies from 1985 to 2020. We uncover three main themes across the previous studies. First, previous research applied a wide range of definitions of the term “entrepreneur”. Second, we identify several inconsistent findings across studies, which may at least partially be due to the use of heterogeneous entrepreneur samples. Third, the few studies that distinguished between various types of entrepreneurs revealed differences between them. Our systematic differentiation between entrepreneur sub-types and our research integration offer a novel perspective that has, to date, been widely neglected in academic research. Future research should use clearly defined entrepreneurial samples and conduct more systematic investigations into the differences between entrepreneur sub-types.

Download Full-text

Start-up and Steady-State Performance of a New Renewable Alcohol-To-Jet (ATJ) Fuel in Multiple Diesel Engines

10.4271/2015-01-0901 ◽

2015 ◽

Cited By ~ 8

Author(s):

Terrence Dickerson ◽

Andrew McDaniel ◽

Sherry Williams ◽

Dianne Luning-Prak ◽

Len Hamilton ◽

...

Keyword(s):

Steady State ◽

Diesel Engines ◽

Start Up ◽

Steady State Performance

Download Full-text