Heterogeneous catalysis: looking forward with molecular simulation

Some of the areas in which we anticipate, over the next five years, notable advances in the application of molecular simulation to problems in heterogeneous catalysis are considered, in the context of recent progress to date. The areas specifically addressed are:

• expanding access to methods,

• quantitative structure-property relationships,

• building structural models to focus or pre-screen experiments,

• confidence in predicting local and extended structure

• reaction mechanisms, barriers and kinetics, and

• data for chemical process simulations.

In each of these areas, we indicate why we consider the topic significant, provide reference to topical work and suggest opportunities for future developments.     

Implementation of ISO 14001:2004 (environmental management system standard) for reverse osmosis desalination plants for the first time in Iran

Implementation of ISO 14001:2004 (environmental management system) has been executed for reverse osmosis desalination plants for the first time in Iran at Noor Vijeh Company (N.V. Co), a water and wastewater firm based in Tehran. The scope of work was the activities and product of company's BWRO desalination plant in the city of Qom (3000 m³ per day) and SWRO desalination plant in Assaluyeh, Pars Special Economic and Energy Zone, Iran. The aims of this project were in line with company’s approach to sustainable development and its direction towards conducting environmental friendly activities and production characteristics.

Initially the famous PDCA (Plan, Do, Check, Act) was used to identify the aspects and evaluate their effects. The significant aspects of each plant affecting the environment are then identified and preventive control measures and reducing their probabilities of loss are anticipated. These cover the normal activities within each plant and those aspects arising from emergency conditions such as earthquakes, fire, etc.

Elements of this system are

• Environmental policy and its targets and programmes

• Practical methods for environmental management system processes

• Executive manuals for implementing special activities

• Tables and indexes for environmental aspects for each plant

• Organizational charts, positions, qualifications, and necessary trainings for the involved personnel.

Environmental aspects are evaluated through their interaction with and effects over, releases to water, emissions to air, land contamination, waste management, energy use, and use of natural resources and raw material.     

On the reduction of desalting energy and its cost in Kuwait

All seawater desalting processes, multi-stage flash (MSF), multi-effect boiling (MEB), mechanical vapor compression (MVC) and seawater reverse osmosis (SWRO) consume significant amounts of energy. The recent increase of fuel oil cost raises the cost of energy consumed for desalting water and the final water cost, and creates more interest in using more energy efficient desalting systems.

The most used desalting systems by distillation (MSF and MEB) are usually combined with power plants in what is called co-generation power desalting plants, CPDP. Fuel is supplied to the CPDP to produce both desalted water D and power W, and the fuel cost is shared between D and W. Exergy analysis and equivalent work are among the methods used to determine the fuel energy charged to each product. When desalting systems, such as SWRO and MVC, are not combined with a power plant, the fuel energy can be directly determined from its electrical power consumption.

In this paper, the fuel energy cost charged to desalting seawater in the presently used CPDP in Kuwait is calculated based on exergy analysis. The MSF, known by its high energy consumption, is the only desalting method used in Kuwait. The MSF units consume 258 kJ/kg thermal energy by steam supplied to the brine heater BH, 16 kJ/kg by steam supplied to steam ejectors, and 4 kWh/m3 mechanical energy for pumping. These MSF units are operated either by:

(1) Steam extracted from extraction/condensing steam turbines EC/ST as in as in Doha West, Azzour, and Sabbiya CPDP. This practice is used in most Gulf area.

(2) Steam supplied directly from boilers as occurred in single purpose desalting plants as Al Shuwaikh plant; or in winter time when no steam turbines are in operation in the CPDP to supply steam to the desalting units.

The CPDP have limited water to power production ratio. While they can cope with the increase of power demand, it cannot satisfy the water demand, which is increasing with higher pace than the power demand.

The case of steam CPDP used in Kuwait is presented in this paper as a reference plant to evaluate the amount of fuel energy consumed to desalt water in MJ/m3, its cost in $/m3. The resulted high fuel cost calls for some modifications in the reference CPDP to lower the energy cost, and to increase its water to power ratio. The modifications include the use of an auxiliary back-pressure steam turbine ABPST supplied with the steam presently extracted to the MSF units. The power output of the ABPST operates MVC or SWRO desalting units; while the ABPST discharged steam operates LT-MEB desalting unit. The desalting fuel energy costs when applying these modifications are also calculated by the exergy analysis and compared with that present situation.

It is also suggested to increase desalted water output by using separate SWRO desalting units operated by the existing power plants of typical η_c = 0.388, or by new combined gas/steam turbines power cycle GT/ST-CC of typical η_c = 0.54 under construction. The SWRO with energy recovery is assumed to consume typical 5.2 kWh/m³ electric energy.     

Pilot filtration study to reduce fouling on Marbella seawater RO plant

The seawater RO plant at Marbella had operated intermittently, and at low flowrates, since its construction 10 years ago. This was because the plant had been designed to operate at times of water shortage, to provide water when the conventional supplies were not available.

During the early part of the 21st century, the mode of the plant changed, and it was expected to operate at design capacity for most of the time. This brought two facts to light — that during high abstraction rates the intake water quality deteriorated significantly, and that the filtration system that had been installed was not capable of adequately filtering the feed water to make it suitable for feeding to a reverse osmosis plant.

The plant was originally built using DuPont B10 permeators. Due to the unavailabilty of these permeators, the plant is currently being converted, stream by stream, to spiral wound membranes supplied by Hydranautics.

At design flowrates, the DuPont system fouled rapidly, and required cleaning every two weeks. The spiral trains fouled more slowly, but still required cleaning at a higher frequency than would be considered normal for this type of plant.

A pilot filtration plant was installed on site to attempt to find the following;

• An optimum coagulant for the water.

• An approximate dose rate for that coagulant.

• The effect of different media on the quality of filtered water.

• The length of run between backwashes using different media.

• The quality of water that can be achieved using this coagulant and media.

By installing pressure tapping points along the length of the filter, the area of differential pressure could be measured. This was used to ensure depth filtration was taking place, and the foulants were being removed through the length of the bed rather than surface filtration.

The trials lasted a total of three months and achieved all of the targets set. The SDI typically achieved by the main plant was approximately 5. The pilot filter showed that the SDI could be reduced to below 2 by modifying the filters and applying a coagulant. Filter runs achieved by the pilot filters were in excess of 48 h.

Following the trials, the plant commenced replacing the media in the filtration system, and is expected to install a coagulant dosing system once this was complete.

This paper describes the pilot plant built, the selection of the media, and the coagulants used, and presents the operating data produced from the trials.     

Application of infrared ATR spectroscopy to in situ reaction monitoring

The infrared horizontal ATR technique was adapted to be applied for in situ reaction monitoring even at high pressure and high temperature. Different types of reactors and flow cells were built which can be used for recording IR ATR spectra at pressures up to 200 bar and temperatures up to 300°C.

The use of the horizontal ATR technique is shown by the following application examples:

• addition reaction of n-butyl isocyanate with butyric alcohol;

• investigation of the equilibrium of isocyanate, HCl and carbamic acid chloride at elevated pressure and temperature;

• monitoring the polycondensation of bifunctional alcohols and carbonic acids;

• recording spectra of polymer melts at 280°C.

Teaching and learning strategies and evaluation changes for the adaptation of the Chemical Engineering degree to EHES

An integrated learning methodology has been developed and implemented in order to adapt the Chemical Engineering degree in the University of Valladolid (Spain) to the European Higher Education Space (EHES) philosophy. It was necessary to modify the objectives and theoretical contents of the different subjects and also the learning methodology, considering the general chemical engineering skills and also the transferable skills reached by the students, according to the recommendations of the European Federation of Chemical Engineering (EFCE) for chemical engineering education in Bologna two-cycle degree system.

This methodology has been applied to the seventh semester of a 5 years Chemical Engineering degree. The main objectives of the proposed strategy were:

• To provide to the student with a holistic, integrated and applied vision of the different subjects involved in chemical engineering, coordinating all of them and planning common activities as a case study based on an industrial process.

• To help students to develop transferable skills by means of designing suitable teaching and learning strategies.

• To prepare the students for the long-life learning.

General and particular objectives were defined adapting the course to the EHES philosophy. In this sense, the programmes in terms of the learning outcomes and competences to be acquired were designed, the total student workload to get the objectives of the programme was estimated and the entire course was programmed and planned in a detailed schedule. A course guide was elaborated including all this information, resulting in a useful instrument for teachers and students.

This methodology was complemented with the evaluation of the global learning process. The evaluation made was based on the next two aspects:

• Student learning evaluation. Tutorial sessions, written reports, oral presentations, discussion sessions and partial and final written exams were considered.

• Learning methodology evaluation. External evaluation requires carrying out inquiries, both to students and teachers involved.

Optimal design of hybrid RO/MSF desalination plants Part III: Sensitivity analysis

This is the last paper in a series of three parts entitled “Optimal design of hybrid RO/MSF desalination plants”. This research is concerned with exploring the feasibility of hybridization of multi-stage flash (MSF) and reverse osmosis (RO) technologies in order to improve the performance characteristics and process economics ofthe conventional MSF process. The research project involved an optimization study where the water cost perunit product is minimized subject to a number of constraints. In the first part, the design and cost models were presented, the optimization problem formulated and solutions for a number of cases were outlined. In the second part, results were presented and discussed. In this paper we discuss the sensitivity of water cost from the alternative plant designs to variations in some cost elements and operating conditions. In general, it is concluded that, for the same desalting capacity, hybrid RO/MSF plants can produce desalted water at a lower cost than brine recycle MSF plants, while hybrid plants are characterized, by lower specific capital costs and higher water recovery fractions. Reduction in steam cost allows MSF to compete more with hybrid RO/MSF plants. This result explains the advantage of coupling MSF plants and steam power plants where the exhaust steam from the back pressure turbine represents a relatively cheaper source of heat for the MSF process. Results showed that the RO technology exceeds all other designs over the whole range of energy, chemicals and membrane costs studied here. However, water cost of the RO process was the most sensitive to variations in membrane and electricity costs compared to other hybrid configurations.     

Energy and water in Kuwait: A sustainability viewpoint, Part II

In Kuwait, the daily consumption per capita of electric power is 14,000 kWh, and of desalted water is 600 L. These are among the highest in the world, and the total consumption of each is almost doubled every 10 years. The cogeneration power desalting plants CPDP producing these two commodities consumed about 54% of the total 150 millions barrels of fuel consumed in the year 2005. If these consumption and production patterns prevail, the fuel oil produced in the country can be fully consumed locally in 30 years, with nothing left for export, the main source of income. The picture can be changed if better desalted water and power production methods are used. These include changing the desalting method from multistage flash MSF known by its high energy consumption to the more energy efficient seawater reverse osmosis SWRO; and power production method of steam or gas turbine cycles to combined gas/steam turbine combined cycle known of its high efficiency. The energy consumed by the air conditioning AC systems should be reduced by using better codes of building insulation and more efficient AC systems. Other conservation methods to reduce water consumption and the energy consumed by transportation are outlined in this paper.     

Two detailed case studies of large Libyan desalination plants and their influence on development

Two large Libyan desalination plants are studied :

1. The Ganzour (Tripoli West) MSF plant with two units, each having a rated distillate output of 11,250 m³/day at full load, the distilla- te purity being 25 ppm. The reliability tests on this plant are just beginning and consequen- tly we shall stress on the erection problems.

2. The Zliten MSF plant with three units, each having a distillate production rate of 4525 m³/day, the distillate purity being 25 ppm. This plant being in operation, we shall stress on the occuring maintenance problems.

All difficulties encountered (during erection for Ganzour plant and during maintenance for Zliten plant) are studied in details. Also the influence of each plant on the development of surrounding regions is considered. Recommendations to both sides (Libyan government and foreign plant manufacturers) are made in order to avoid the future repetition of these problems and troubles.     

Construction and commissioning of 6 × 23,000 T/D MSF plant,Al Jobail phase 1

This paper outlines the construction and operational experience with 6 × 23,000 tons per day multi-stage flash desalination plants which were installed at Al-Jobail, Kingdom of Saudi Arabia.Module transporation and construction was adopted on this project to get the high quality of evaporator manufacture at shop and to shorten the construction period at site.During the reliability test f each evaporator unit, various types of antiscale chemicals were applied to compare the performance results. Extended operaton was also done to obtain long term performance results which might be applied as design criteria for other MSF evaporators.     

Low temperature reject heat utilization for desalination; Economical and technical aspects

The economics of medium and large sized (1'000…10'000 m³/d) MSF/ME plants which utilize reject heat at temperatures between 50…90 °C is investigated.It is shown that for a cogeneration plant based on the Rankine cycle in combination with an evaporative desalination plant, there exists a steam condensation temperature (60…80 °C) below which the water production of the cogeneration plant is higher than the production of a power equivalent reverse osmosis plant. Power equivalent means, that the reverse osmosis plant would utilize the electricity otherwise lost when the same Rankine cycle is operated at higher condenser temperature. In spite of the higher investment costs for the evaporative plant, the specific water costs are lower than those for the power equivalent RO plant. Using a Rankine cycle for cogeneration, optimization of reject heat temperature levels is therefore crucial for obtaining economically favourable conditions.Further it is shown, that for todays and assumed future electricity rates and oil prices, the MSF/ME when powered by diesel reject heat produces cheaper water than RO or VC plants. It is necessary however, that the MSF/ME can cope with the inevitable load variations of the diesel power station. Our companys contribution in this field is briefly described.     

Investment costs and energy consumption of the MSF/FBE in comparison with the MSF

The use of the MSF process in seawater desalination is broad because of simplicity and reliability and an improvement of this process has been proven in the use of the fluidized bed heat exchanger. The choice of most economical gain ratio of a multi-stage flash evaporator is very dependent on energy cost, i.e. steam-and electricity cost. Because of lower investment and electricity costs the MSF/FBE has always lower product water cost than the MSF with equal gain ratio.     

Numerical simulation and analysis of a patented desalination and power co-generation cycle

A patented cycle for water desalination and power generation was evaluated with regard to thermal efficiency and water production. The inventor of the patent claimed that the patented cycle provides a thermal efficiency of 41 %, which is higher than current combined water and power generation steam plants. A simulation program was developed to evaluate the thermal efficiency and water productivity of this cycle. Simulation parameters were selected from data provided by the patent as well as data generally used in the design of combined power and desalination plants. Results of the simulation were compared with a simulation of the Jubail-II combined plant. The simulation proved that the patented cycle is far inferior to current dual-purpose MSF desalination plants in terms ofwater production. In addition, the patent was found to have a much lower efficiency than what was claimed by the inventor.     

Nucleation in the flash boiling of sea water

Some results from an experimental investigation into the mechanism of bubble nucleation in the flash boiling of water are presented. Conditions similar to those found in polyphosphate dosed MSF plants have been studied. The experiments suggest that the naturally occurring nucleation sites in sea water give an effective site radius of the order of 15–20 microns. Such sites with the help of dissolved gases would be effective only over the top quarter of the flash range in a typical plant. Diffusion of gas towards the sites is thought to be responsible for the time delays of the order of seconds between decompression and nucleation.     

An integrated self sufficient multipurpose plant for seawater desalination

A multipurpose plant is described, which produces drinking water and chemicals from seawater. The most important part of the plant consists in a combined MSF/VT evaporator, which operates on a high economy ratio and enables also a high concentration of the brine. These two facts are due to a special treatment of the evaporator feedwater by chemical agents produced from the concentrated brine. A surplus of these chemicals can be sold. The energy supply of the complex is assured by an adequate power station, which provides process steam and electricity at such a ratio as to minimize fuel cost.     

考虑水需求的水电联产海水淡化系统的优化设计

水电联产不仅能缓解淡水资源不足的问题,而且可有效降低能耗和淡化成本。建立了水电联产系统数学模型,将优化设计描述为一个混合整数非线性规划(MINLP)问题,并采用混合编码的遗传算法进行求解,结果表明,以水定电模式下水电联产系统最优操作模式为发电、多级闪蒸(MSF)和反渗透(RO)三者的集成,且MSF和RO的产水比存在最优值,发电采用背压式蒸汽轮机。随着淡水需求量的增加,联产系统的淡水成本逐渐降低,MSF与RO的产水比呈现出逐渐降低的趋势。     

多级闪蒸过程的热力学效率及低位热能的利用条件

本文从分析多级闪蒸过程的不可逆性出发,建立了加热过程和盐水循环多级闪蒸过程的可用能损失关系;讨论了余热利用的条件;并提出反映多级闪蒸系统热力学效率的不可逆温差函数.提供了评价该类装置热力学效率以及过程改进方向的方法.利用上述原理对一台5级海水淡化实验装置和大型生产设备的能源利用进行评价,结果表明:本文的方法可用于按节能原则选择闪蒸级数、传热端差和相对流量等过程参数.