Total Steam Research Articles

Opportunities for process-integrated evaporation in a hardwood pulp mill and comparison with a softwood model mill study

Significant energy savings can be made in the pulp and paper industry by implementing process-integrated evaporation (PIvap). The aim of this paper was to evaluate the concept of PIvap for a existing hardwood mill producing kraft pulp and compare the results with the ones from an earlier study of a softwood model mill. Using pinch tools, we found a solution where 1.3 GJ/ADt of pinch violations are solved and 1.1 GJ/ADt of excess heat is extracted. If the excess heat is used in an efficient PIvap, steam savings of 2.7 GJ/ADt could be made in the evaporation plant. Together with the pinch violations and improved soot blowing, the total steam savings were 4.6 GJ/ADt or 36% for an investment cost of 6.6 M€. Compared with the softwood model mill, the configuration of the hardwood mill offered about the same savings with 2.7 M€ lower investment cost, making PIvap more interesting in the hardwood mill. As an alternative to implementing PIvap, more pinch violations can be solved. The PIvap approach gives more steam savings to approximately the same specific cost.

Crescimento inicial de <i>Pinus taeda</i> L. relacionado a doses de N, P e K.

O presente trabalho teve como objetivo estudar os efeitos de diferentes doses de N, P e K no crescimento inicial de plantas de Pinus taeda, aos 19 meses de idade. O experimento localiza-se próximo do Município de Cambará do Sul, tendo como coordenadas UTM "centrais" 565125 E e 6777386 N. O solo da região é classificado como Cambissolo Humico alumínico típico, textura argilosa. A metodologia estatística utilizada foi a técnica do confundimento, para três fatores, com quatro níveis, totalizando 64 tratamentos, distribuídos em quatro blocos. Foram medidas as seguintes variáveis no campo: altura total, altura de copa, diâmetro à altura do colo e diâmetro de copa. Os resultados indicam que foi obtida resposta linear e quadrática significativa para o P, evidenciando a importância da aplicação desse nutriente no crescimento inicial das plantas de Pinus taeda, com máximo ganho em volume cilíndrico, nas doses de 64 e 87 kg ha-1 de P2O5 e K2O respectivamente.

Investigation of ethanol conversion for hydrogen fuel cells using computer simulations

AbstractEthanol conversion to hydrogen has been investigated by a series of thermodynamic analyses and computer simulations within the context of a cost‐effective fuel processor/fuel cell system where heat exchange is of great importance. Two different methods, multi‐reaction equilibria and Gibbs free energy minimisation, are used for the thermodynamic analyses. The computer simulations consider the catalytic conversion of ethanol to hydrogen on a bimetallic Pt–Ni catalyst by indirect partial oxidation (IPOX) which consists of total oxidation (TOX), steam reforming (SR) and water–gas shift (WGS) reactions. The results indicate that there is an optimal water:fuel ratio for maximum hydrogen production at each operating condition for hydrogen yields calculated as a percentage of the theoretical value. Mass‐based hydrogen yields are also presented considering fuel economy especially for vehicular applications. Finally, the benefits of using a secondary WGS reactor and the comparison of the results of the two thermodynamic methods are highlighted. Copyright © 2005 Society of Chemical Industry

Remediation of a chlorinated solvent-contaminated site using steam injection and extraction

The remediation methods designed and deployed for use at the Department of Energy Savannah River Site 321-M solvent storage tank area (SSTA) comprise a complete set of cleanup and control techniques using steam remediation and electrical resistance tomography. The technologies include the engineered combination of steam injection; dual-phase extraction for subsurface remediation; and an in-situ tomographic imaging technology for monitoring of thermal treatment zones in the subsurface. The technologies use methods developed for enhanced oil recovery using steam injection.At the SSTA, the remediation zone was 31 31 m (100 100 ft) on the surface and extended from 6- to 49-m (20- to 160-ft) depth. The ambient water table exists at approximately 44-m (145-ft) depth. Steam injection wells ringed the target zone, with multiphase extraction dominated by a centered dual-phase extraction well, with three additional existing perimeter vapor extraction wells.The SSTA field-scale deployment of steam injection, groundwater pumping, and vapor extraction removed 31,000 kg (68,000 lb) of volatile organic compounds during 12 months of operation. Total steam injected for the 12-month period of operations was approximately 48 109 kJ (45 109 BTU), injected at wellhead pressures between 0.15 and 0.38 MPa (7 and 40 psig), depending on lithology of the screened interval, depth, and operational considerations.

Rhenium Oxidation by Steam at High Temperatures

The kinetics of rhenium oxidation were studied under flowing steam+argon mixtures, at atmospheric total pressure and steam partial pressure in the range 24–74 kPa, and at temperatures from 1600°C up to 2200°C. No regime change was observed in the temperature dependence of the oxidation rate, which shows that the same chemical regime extends up to the highest temperature investigated. Moreover, at high temperature, the results showed a dependence of the oxidation rate on the gas velocity and the steam partial pressure, in good agreement with a gas-phase mass-transfer correlation for laminar flow, revealing that, for the conditions used, mass-transport processes in the gas phase also act as a limiting factor. It was assumed that the mass-transport limiting factor is the steam diffusion through a volatile oxides gaseous layer above the rhenium surface. A comparison of these results with rhenium oxidation rates reported for air leads us to propose the dissociative adsorption of the H2O molecule as the limiting chemical stage of the oxidation process.

Steam Turbine Versus Pressure Reducing Valve Operation

ABSTRACT A question arising frequently in steam system design relates to the benefits and drawbacks associated with passing steam through a pressure reducing valve or a steam turbine to supply a low pressure steam demand. The most appropriate analysis of the economic benefits of operating the steam turbine utilizes an incremental systems approach. A case study analysis based on a systems approach was used to demonstrate the role of incremental fuel and electricity costs, boiler and turbine efficiencies, as well as steam flow and thermodynamic properties on the economic performance of the turbine-generator and pressure reducing valve options. An example analysis was performed for a boiler producing superheated steam at 600 psig and 800°F to supply a low pressure steam demand of 30,000 lbm/hr. Overall energy balances were computed for a turbine with an isentropic efficiency of 40%, a 90% efficient generator and an isenthalpic pressure-reducing valve as an alternative scheme. For a fuel unit cost of $3.00/106 Btu and an electricity unit cost of $0.035/kWh, it is shown that 408 kW of electricity can be produced while supplying the steam demand. Use of the turbine-generator requires the total steam flow rate to increase to satisfy the process heating demand. The steam flow through the turbine would be 31,261 lbm/hr or about a 4% increase over the lowpressure process base load. Assuming that the modest additional highpressure steam demand can be met, a net purchased energy saving of $70,000/yr. could be realized. This analysis demonstrates that a substantial plant-purchased energy cost saving may be achieved for typical system operating conditions when a turbine-generator is used to produce low-pressure process steam rather than a pressure reducing valve.

STEAM T URBINE V ERSUS P RESSURE REDUCING V ALVE O PERATION

A question arising frequently in steam system design relates to thebenefits and drawbacks associated with passing steam through a pres-sure reducing valve or a steam turbine to supply a low pressure steamdemand. The most appropriate analysis of the economic benefits of op-erating the steam turbine utilizes an incremental systems approach.A case study analysis based on a systems approach was used todemonstrate the role of incremental fuel and electricity costs, boilerand turbine efficiencies, as well as steam flow and thermodynamicproperties on the economic performance of the turbine-generator andpressure reducing valve options. An example analysis was performedfor a boiler producing superheated steam at 600 psig and 800 °F to sup-ply a low pressure steam demand of 30,000 lbm/hr. Overall energybalances were computed for a turbine with an isentropic efficiency of40%, a 90% efficient generator and an isenthalpic pressure-reducingvalve as an alternative scheme. For a fuel unit cost of $3.00/10 6 Btuand an electricity unit cost of $0.035/kWh, it is shown that 408 kW ofelectricity can be produced while supplying the steam demand. Use ofthe turbine-generator requires the total steam flow rate to increase tosatisfy the process heating demand. The steam flow through the tur-bine would be 31,261 lbm/hr or about a 4% increase over the low-pressure process base load. Assuming that the modest additional high-pressure steam demand can be met, a net purchased energy saving of$70,000/yr. could be realized. This analysis demonstrates that a sub-stantial plant-purchased energy cost saving may be achieved for typi-cal system operating conditions when a turbine-generator is used to produce low-pressure process steam rather than a pressure reducing valve.

Evaporation of black liquor and wastewater using medium-pressure steam: Simulation and economic evaluation of novel designs

In this paper, novel evaporation plant designs that use medium-pressure steam and deliver low-pressure (LP) steam to the steam network as well as conventionally designed plants are simulated and evaluated from a technical and economic point of view. Both evaporation of black liquor only and combined evaporation of black liquor and wastewater are analyzed. The results show that the novel designs suggested in this work all have large potential to save live steam and that an additional 8 m 3 of wastewater/ADMT (air dry metric ton) can be evaporated without increasing the mill’s total live steam demand. They also indicate that the demand for LP steam in the rest of the process is less important for the savings in live steam. The total cost for the novel designs and the relationship between that cost and the cost for conventional designs depend on the economic conditions assumed. If the investment in a more energy efficient evaporation plant is considered from a strategic point of view using an annuity factor of 0.1 and if the cost of the saved fuel is rather high in comparison to the electricity price, the total cost for the novel designs will have a lower total cost than the traditional designs.

Dynamic modelling and scheduling of an industrial batch system

This paper addresses the optimal schedule of a resource constrained four-batch digester system of an industrial acid sulphite pulp mill. This involves the development of two different models, one to model the scheduling operational problem and the other the batch digester operation—process model. The first model uses a discrete-time Resource Task Network (RTN) based representation leading to a Mixed Integer Linear Program (MILP) formulation. In this, the main operational limitation, steam availability, is modelled through the definition of a superstructure including the most relevant heating alternatives. The duration of the generated heating tasks was estimated through the use of the process model—a distributed heterogeneous dynamic model in gPROMS, with a heat-transfer resistance at the solid–fluid-interface—validated with experimental plant data. The optimal schedules obtained showed that an increase in the total available steam from the boiler is vital to allow a higher level of productivity and that not much can be done regarding steam sharing improvements.

ECONOMIC LOAD ALLOCATION

The presented algorithm provides solution of the economic load allocation (ELA) problem, minimizing total steam production costs, as well as dynamic allocation. The total fuel feed trajectory demand is provided by a predictive master pressure controller which controls pressure in a common steam header. Application of a model-based predictive controller as the master pressure controller provides additional features to the allocation algorithm: fuel flow at the end of the prediction horizon is used as an estimate of the steady state value for evaluation of the economic allocation, while the transient part can be allocated independently.

On-board fuel conversion for hydrogen fuel cells: comparison of different fuels by computer simulations

The conversions of methane, propane, octane and methanol to hydrogen under conditions pertinent to fuel cell operation have been described quantitatively and examined by a series of computer simulations. Catalytic conversion may be achieved by direct partial oxidation or by a combination of total oxidation and steam reforming. Both systems have been simulated, using conversion data and kinetic equations reported in the literature for various catalyst configurations and hydrocarbons. The results show that, in terms of hydrogen produced per weight of fuel and water carried, direct partial oxidation of propane or oxidation/steam reforming of octane are the best alternatives. The latter possess the ease of operation but coke formation may be more of a problem. Methanol, often suggested as a fuel, is much less efficient. Operation of a vehicle using the catalytic conversion system would require fueling by both hydrocarbon and water.

Steam System Improvement in a Food Processing Plant: A Case Study

ABSTRACT This article discusses the findings of a survey which was conducted in a food processing plant. The study focuses on the steam system. The process includes raw material preparation, cooking, frying and packaging. The frying and cooking processes utilize steam. The annual steam cost at this food processing plant is approximately $1.2 million dollars. The plant does not generate steam but purchases it from an outside utility plant at 400 psig. In the plant, steam is utilized at various pressures, ranging from 10 psig to 400 psig. The food processing plant utilizes pressure reducing valves to supply steam at various pressures lower than 400 psig. The 400 psig steam users utilize more than 80 percent of the total steam supplied. The various steam users at lower pressures utilize the remaining quantity of steam. All of the condensate is collected in an atmospheric flash tank before being sent back to the outside utility plant. An electric motor-driven pump returns the condensate to the outside utility. The study identified several steam cost saving opportunities. The saving opportunities included improvements in the steam utilization and the condensate return system. Steam pressure is reduced from high pressure to supply the lower pressure users. On the other hand, the high pressure condensate is flashed to atmospheric pressure. The lower pressure steam users can utilize flash steam that is produced from the high pressure condensate. In this way, the food plant can reduce the quantity of purchased steam and minimize the quantity of flash steam being released to the atmosphere. Upon the implementation of the proposed measures, the food plant can save 10 percent of the its annual steam cost. The average payback period to implement the identified saving measures is less than 3 years.

Steam System Improvement in a Food Processing Plant: A Case Study

ABSTRACT This article discusses the findings of a survey which was conducted in a food processing plant. The study focuses on the steam system. The process includes raw material preparation, cooking, frying and packaging. The frying and cooking processes utilize steam. The annual steam cost at this food processing plant is approximately $1.2 million dollars. The plant does not generate steam but purchases it from an outside utility plant at 400 psig. In the plant, steam is utilized at various pressures, ranging from 10 psig to 400 psig. The food processing plant utilizes pressure reducing valves to supply steam at various pressures lower than 400 psig. The 400 psig steam users utilize more than 80 percent of the total steam supplied. The various steam users at lower pressures utilize the remaining quantity of steam. All of the condensate is collected in an atmospheric flash tank before being sent back to the outside utility plant. An electric motor-driven pump returns the condensate to the outside utility...

Simulation of the catalytic partial oxidation of methane to synthesis gas

The modeling and simulation of reactors for the catalytic partial oxidation of natural gas to synthesis gas is complex and requires detailed kinetics if it is to be representative and reliable. Adiabatic fixed bed reactors with a catalytic combustion zone fed with methane/oxygen or methane/air mixtures were simulated based upon the kinetics of total combustion, steam reforming and water-gas shift on a Ni catalyst. The steam reforming reactions and water-gas shift reaction are parallel or more or less consecutive to the total combustion, depending upon the degree of reduction of the catalyst, which is determined by the temperature and the gas phase composition. The calculation of the net rates of coke formation was included in the simulation. The influence of carbon dioxide and steam was also investigated.

Turning to supply-side management: Estimating industrial cogeneration potential

Increased recognition by electric utilities of the economic opportunities for load displacement or purchase of customer cogenerated electricity has initiated a change in utility supply-side planning that has parallels with demand-side management activities. Analytical tools and detailed research are required to forecast the technical, economic and industry-offered cogeneration potential from various sources. In this study, an end-use technology simulation model (ISTUM-I) is used to estimate the future incremental cogeneration potential from pulp and paper mills in British Columbia under different scenarios of industry evolution. The estimated technical potential of 5000 GWh (815 MW) results from determining the total process steam requirements and highest feasible boiler pressures. The economic potential of about 3500 GWh (570 MW) depends upon the social discount rate, the utility's long run avoided costs, boiler cost estimates and the value of burning wood waste that must otherwise be disposed of. The industry-offered potential of 1200 GWh (200 MW) results from behavioural parameters in the model that mirror past investment decisions. As with demand-side management, various strategies are available to the utility to bridge the gap between industry-offered and economic potential.

Response to Severe Changes of Load on the Reactor System of Nuclear Ship Mutsu.

Abstract The response of the nuclear power system of N.S. Mutsu to severe changes of load have been studied from records taken during the power-raising tests performed on the ship in 1990. The records examined were those involving the most severe load changes foreseen for marine reactors : (a) sharp load increase with total steam flow raised from 25 to 70% rated full flow in 13 s, (b) crash astern maneuver with the position of propulsion turbine command handle changed—taking several seconds—from cruising ahead to STOP, and after about 50 s, further changed—taking 30 s—to bring the astern propulsion turbine to full speed—to consume approximately 60% rated total steam flow and (c) turbine trip with the ahead turbine intentionally tripped when operating at roughly 100% rated total steam flow. The foregoing records from load changes—of severity beyond what is foreseen for land- based reactors—proved that the Mutsu reactor is capable of responding smoothly and securely to such severe load changes. These load c...

Steam Consumption Control System for Batch Pulp Cooking

Abstract In batch pulp cooking the heating steam is used only in some phases of the technological procedure. This causes very irregular total steam consumption. High steam flow-rate variations impose a high dynamic load at the steam generation plant which reduces the efficiency of the steam generation. In this contribution a system for steam consumption control is presented, which is based on the three multiloop microprocessorbased controllers. The implemented control structure consists of a set of temperature controllers, a set of “smooth”temperature set-point generators, a set of state-machine algorithms for sequential control, a steam distribution algorithm, a simple steam flow-rateestimation and a steam flow-rate controller. The control structure is simple enough to allow the implementation as a stand-alone small-size control system. The lowcost solution is provided also by elimination of the need for aseparate steam flow-rate measuring system for each digesterʼs heat exchanger. After the installation a reduction of 70% in steam flow-rate variance was measured. The reduction may be adjusted by the operator as a compromise between the acceptable dynamic loading of the steam boilerand the requested pulp production rate.

Ibuprofen, allopurinol and lipid peroxidation

The dynamic changes in blood gases in 34 dogs suffering severe steam inhalation injury were studied during the first 14 days post-burn to determine the effects of inhalation injury on lung function. Nineteen dogs received only severe steam inhalation injury, while 15 other dogs received both 30 per cent total body surface area (TBSA) deep burns and steam inhalation injury.The results showed marked reductions of Pao2, Paco2, AB, SBE, T-CO2, SB, BBp, pHNR and Sato2 (P<0.05∼0·01), whereas the P(A-a)o2 increased (P<0.05∼0·01) within week 1 post-burn in both groups. These data suggest that the injured animals were suffering from hypoxaemia and respiratory alkalosis induced by disturbance of the gas-exchange function of the lungs. There was also metabolic acidosis. which was closely related to high fever, excessive catabolism, and particularly to hypoxaemia in week I postburn. If the animals survived through the critical period (1–7 days post-burn), most of the abnormal gas parameters then gradually returned to the pre-burn levels. It is clear, therefore, that blood gas monitoring in patients with inhalation injury is not only of diagnostic importance but also of prognostic value.

Evaluation of reservoir model predictions for the olkaria east geothermal field, kenya

In 1984 a detailed three-dimensional well-by-well model was developed for the Olkaria geothermal field in Kenya. The model was calibrated against the production history of the field over the period 1977–1983, using porosity and permeability as adjustable parameters. During this period two 15-MW c Units were put on-line at Olkaria; the third 15 MW c Unit commenced operation in March, 1985. The numerical model was used to predict the performance of the Olkaria wells, and these predictions have been compared with the observed well behavior for the period 1984–1987. In general, the model predictions show satisfactory agreement with the observed well behavior, especially for those wells that had production histories exceeding two years. The predicted steam rates for most of the wells were accurate to within 1 kg/s for the period considered, and the steam rate decline was well-predicted by the model. Some differences between the observed and predicted total flow rates and enthalpies of individual wells were seen, especially in those wells with large enthalpy variations or unorthodox increases in total How rate. The model also predicted that three make-up wells would he needed by the end of 1987. which is consistent with the observed decline in total steam rates. New performance predictions have been made using an updated model, including the effects of wastewater reinjection.

Blood gas studies in dogs with severe steam inhalation injury

The dynamic changes in blood gases in 34 dogs suffering severe steam inhalation injury were studied during the first 14 days post-burn to determine the effects of inhalation injury on lung function. Nineteen dogs received only severe steam inhalation injury, while 15 other dogs received both 30 per cent total body surface area (TBSA) deep burns and steam inhalation injury. The results showed marked reductions of Pao 2, Paco 2, AB, SBE, T-CO 2, SB, BBp, pH NR and Sato 2 ( P<0.05∼0·01), whereas the P(A-a)o 2 increased ( P<0.05∼0·01) within week 1 post-burn in both groups. These data suggest that the injured animals were suffering from hypoxaemia and respiratory alkalosis induced by disturbance of the gas-exchange function of the lungs. There was also metabolic acidosis. which was closely related to high fever, excessive catabolism, and particularly to hypoxaemia in week I postburn. If the animals survived through the critical period (1–7 days post-burn), most of the abnormal gas parameters then gradually returned to the pre-burn levels. It is clear, therefore, that blood gas monitoring in patients with inhalation injury is not only of diagnostic importance but also of prognostic value.