Showing papers in "Chemical Engineering in 1995"

For your next separation consider adsorption

Abstract: Adsorption is a separation process in which certain components of a gaseous or liquid phase are selectively transferred to the surface of a solid adsorbent. It can perform many separations impossible or impractical by more familiar techniques such as distillation, absorption, and membrane-based systems. Its importance has been rising in process and environmental applications alike--many new such applications have in fact been made possible by advances in adsorption technology itself. Selecting the right adsorbent for a given separation can make a big difference in how well the adsorption unit performs. Making the selection task especially important is the continual development of new adsorbents. The discussion in this article of practical principles of adsorption puts special emphasis on information helpful for adsorbent selection. Adsorption most often takes place in a fixed bed of adsorbent. The typical arrangement consists of two beds placed in parallel so that tone can be regenerated while the other is adsorbing. Regeneration methods are discussed below.

A potpourri of equipment prices

Abstract: We offer data for a broad range of equipment, including that with hard-to-find costs. The equipment consists of: plate-and-frame heat exchangers, cooling towers, spray dryers, miniature shell-and-tube heat exchangers, process vessels, plastic tanks and their accessories, flares, refrigeration units, gas absorbers, and ductwork

The many measures of fine particles

Abstract: Particle size is a critical parameter for a variety of operations in the chemical process industries (CPI). For example, the flow characteristics of granular materials, the sintering behavior of metallurgical powders, and the combustion efficiency of powdered coal are influenced to a major extent by particle size. The big push in the ceramics industry today is toward processing of powders at or below the one-micrometer level because use of such fine-grained materials allows tighter control of product properties. Accurate measurement or estimation of particle size is important because the quality and performance of most powder-based products are closely related to the size distribution of the fine particles. The electro-optic data processing revolution has spawned a new generation of particle-characterization equipment based on laser probing of particles systems. Computer-aided analysis of the data has come to play a dominant role. The paper discusses the critical step of sampling, the use of sieving for larger particles, the significance of particle shape, the use of lasers in size classifiers, particle surface properties, permeability techniques, and the need for instrument calibration.

Zero discharge. I: A systematic approach to water reuse

Abstract: Much has changed in the way water is managed today. The rising price of water, prolonged droughts, and environmental regulations make water reduction and reuse virtually essential. Today, most facilities have some program in place. But in the absence of industry standards, how those programs are defined, implemented and executed varies from plant to plant, and from owner to owner. The epitome of water reuse is zero discharge. Although the meaning of the term varies, zero discharge most commonly refers to a facility that discharges no wastewater to surface water. The process of closing up a plant`s water balance is a major undertaking that is not without some risks and drawbacks. Typical problems include: roving maintenance problems; reduced plant reliability; presence of trace chemicals; limits on wastewater concentration are exceeded; and lost water rights. The paper presents an outline for a systematic approach to water reuse.

Three-phase flow? Consider helical-coil heat exchangers

Abstract: In recent years, chemical process plants are increasingly encountering processes that require heat exchange in three-phase fluids. A typical application, for example, is heating liquids containing solid catalyst particles and non-condensable gases. Heat exchangers designed for three-phase flow generally have tubes with large diameters (typically greater than two inches), because solids can build-up inside the tube and lead to plugging. At the same time, in order to keep heat-transfer coefficients high, the velocity of the process fluid within the tube should also be high. As a result, heat exchangers for three-phase flow may require less than five tubes -- each having a required linear length that could exceed several hundred feet. Given these limitations, it is obvious that a basic shell-and-tube heat exchanger is not the most practical solution for this purpose. An alternative for three-phase flow is a helical-coil heat exchanger. The helical-coil units offer a number of advantages, including perpendicular, counter-current flow and flexible overall dimensions for the exchanger itself. The paper presents equations for: calculating the tube-side heat-transfer coefficient; calculating the shell-side heat-transfer coefficient; calculating the heat-exchanger size; calculating the tube-side pressure drop; and calculating shell-side pressure-drop.

Fuel cells make their CPI moves

Abstract: Fuel cells convert fuel gas and air electrochemically into power. The natural propensity of fuel gas at the anode side to react with air at the cathode side forces either the fuel gas or oxygen to ionize. The migration of the formed ions through the electrolyte induces an electric current, producing power. A bipolar plate segregates the reactant gases and provides an electrical connection between adjacent cells. The overall electrical efficiency of a fuel cell is 45--70% (LHV, or low heating value). The cogeneration efficiency, which also credits the additional steam and hot water produced, is 70--90% (LHV). These efficiencies are the highest of all available power-generation technologies. Most importantly, fuel cells can achieve these high efficiencies even at plant capacities as small as a few hundred kilowatts. Fuel cells are essentially pollution-free because they do not involve combustion. There are no waste-water discharges from fuel cell plants. These attributes make fuel cells ideal candidates for a new trend in power generation called distributed power generation. With distributed generation, many small scale factories, hospitals, shopping malls, hotels, airports, gas and water-pumping stations, office buildings, and other power consumers can produce their own electricity. The paper describes the three major typesmore » of fuel cells, their benefits, and their estimated cost to the chemical processing industry.« less

Select the optimum pipe size

Abstract: Simple equations show how to calculate the most economic diameter - the one with the lowest life-cycle cost

The painkiller for batch control headaches

Abstract: The world of batch control is a complicated one, containing many of the issues common to continuous processes, as well as such concerns as complex sequential control, product variation, dynamic scheduling and lot tracking. Many different and poorly structured approaches have been taken to these problems, and communication between vendors and users has been troublesome. The newly defined ISA standard, ``SP88, Part 1: Batch Control Terminology,`` brings a large degree of order to the batch control process. SP88 provides definitions of many of the common elements of batch process equipment and recipe steps. In addition, it provides a methodology for logically arranging batch process control, so that the process is understandable and, most importantly, verifiable. Part 1 of this article introduces the important terms and concepts of SP88 along with recommendations for their implementation. In Part 2, a method is proposed to streamline the process of designing and constructing batch manufacturing facilities.

Dealing with two-phase flows

Abstract: Gas- and vapor-liquid flows through pipework or equipment often pose major difficulties in both design and operation. Typically, two-phase fluid systems are susceptible to flow instabilities, blockages, and pressure and temperature fluctuations. As a result, gas-liquid flows are avoided whenever possible by separating the two phases into individual streams of nearly homogeneous gas and liquid. However, certain process conditions require or inevitably produce two phases. Examples include condensate-return lines flashing into steam, vapor-liquid feed lines entering distillation columns, and refrigerant-return lines that must maintain a specific vapor-liquid ratio for efficient operation. The thermohydraulic behavior of two-phase systems includes variations in pressure drop, flow patterns, and liquid holdup or void fraction. Increasing the pipe diameter reduces the pressure drop for a given flowrate, or alternatively produces an increase in the flowrate for a given pressure drop in a piping system. However, increased pipeline diameters lead to higher costs, and may require installation of more expensive equipment to accommodate the resulting larger slug volumes. There have been numerous improvements in correlations and methods for the prediction of pressure drop in gas-liquid flows. A few of them attempt to take into account the highly complex flow structure of a two-phase flow. One mustmore » keep in mind that the flow structure varies with time and position in the pipework. The paper discusses empirical correlations, pressure drop due to friction, gravity, and acceleration, transitions in flow patterns, liquid inventories, and erosion. 46 refs.« less

Spreadsheets for heat loss rates and temperatures

Abstract: Calculating linear heat-loss rates and the temperatures of fluids flowing in pipes is a common problem for engineering dealing with fluid systems. Hand calculations of these design parameters tend to be tedious and are prone to data-entry errors. However, most engineers today have some spreadsheet software installed on their personal computers. These programs can simplify and speed up design analyses. A previous set of articles described a four-step process for calculating the linear heat-loss rate from a pipe. This article describes a spreadsheet that calculates the linear heat-loss rate, insulation surface temperature and fluid temperature along a pipe, for a given fluid and inlet temperature, insulation material and thickness, casing emissivity, and ambient conditions. The spreadsheet can be easily modified to conduct parametric studies of different insulation materials, thicknesses and casing emissivities, to determine the optimum combination for a given fluid flowrate and inlet temperature, and ambient conditions.

Fight corrosion with plastic

Abstract: As chemical processors run plants longer to meet goals for increased production at lower costs, and use higher temperatures and higher throughputs to boost performance, there are more rigorous requirements for durable, corrosion-resistant equipment. Plastics, elastomers and composites help meet this need by protecting carbon steel equipment, and by providing materials of construction for components and structures. They can preserve product purity and quality by preventing contamination. Of the many polymers and composites that have proven useful for managing corrosion of chemical process equipment, most fit into three categories: barrier linings and coatings; self-supporting structures, which can be made of composites or solid polymers in tanks, piping, valves, pumps and other equipment; and other products, such as seals, gaskets, adhesives and caulks. The paper describes all three types and also remarks on the need for failure analysis.

Process tomography : seeing is believing

Abstract: As the chemical process industries try new ways to optimize their processes, they are taking a closer look at tomography. Already well established in medical diagnostics, the technique has found some CPI applications but has long been considered too expensive and impractical for routine use. Promising to change this perception are recent developments in tomographic sensors, image processing algorithms, as well as data processing. Of particular interest to the CPI is tomography`s ability t provide real-time cross sectional images of conditions inside process equipment, allowing operators to see what`s going on in such opaque regions as packed catalyst beds, multiphase solutions, powder mixers, and fluidized beds. The images contain a wealth of data that can be used to: design equipment, verify simulation models and calculations derived via computational fluid dynamics, monitor fluid flow and environmental conditions, and image velocity profiles. One interesting application is as a way of inspecting radioactive waste drums to decide where they should be sent for permanent storage. Another use being studied is the monitoring of air sparging of contaminated areas.

Industrial solvents step up to the mound

Abstract: In the field of industrial solvents, 1,1,1-trichloroethane is known for its ability to cover the bases. Versatile, the organic chemical is widely used for a variety of applications, from vapor degreasing to cold cleaning. But its number is about to be retired. Under a timetable established by the Montreal Protocol, production of this ozone-depleting compound is scheduled to be phased out by the end of the year. As the deadline approaches, the impact of the inevitable exit of 1,1,1 from the marketplace is being cushioned by three developments: the gradual shutdown of some capacity, exemptions for the continued production of 1,1,1 for certain applications, and the rapid development of alternative solvents. So far, industry observers agree, none of the alternative solvents quite match the performance of 1,1,1. Certainly there is some interest in finding a one-for-one replacement for 1,1,1, but it is not the top priority for companies currently pursuing the development of alternative solvents. Instead, they are focused on creating families of environmentally safe products that closely match the performance of 1,1,1 in specific applications. The paper discusses this technology.

Proven tools and techniques for electric heat tracing

Abstract: Piping systems equipped with poor insulation, and such heat sinks as valves, pipe supports and instruments, tend to lose or gain a large amount of heat whenever there is a significant difference between the pipe and ambient temperatures. Variations in ambient temperatures from freezing winter nights to scorching summer days often affect the extent of heat loss or gain as well. Consequently, the fluid inside a pipe may undergo phase changes (such as freezing or vaporization), and the viscosity can change to adversely affect the fluid`s flow patterns. Heat tracing is a way of maintaining the temperature variation in a pipe within an acceptable range. An external heater is installed on the pipe under the insulation to compensate for heat loss. This external heater is typically called a tracer. The paper discusses stagnant fluids, smaller pipes, prevention of freezing, minimizing temperature swings, reliability, point sensing and control, ambient sensing and control, dead-leg sensing and control, cost estimation, and comparing typical costs.

A crash course in project engineering

Abstract: A successful project follows seven well-defined steps: scoping, approval, design, procurement, construction, commissioning and startup

Air pollution control: Escalate equipment costs

Abstract: During fiscal year 1994, this author used the Bernard J. Steigerwald Opportunity for Independent Study, sponsored by US Environmental Protection Agency`s Office of Air Quality Planning and Standards (Research Triangle Park, N.C.), to develop a group of quarterly indexes for adjusting or escalating air pollution control costs from one period to another. In all, nine indexes were developed, one equipment cost index (ECI) for each of nine control device categories. For convenience to the reader, additional indexes for two other equipment categories--available as part of the Producer Price Indexes compiled by the US Bureau of Labor Statistics--are also presented here. These 11 indexes--collectively known as the Vatavuk Air Pollution Control Cost Indexes (VAPCCI)--can be used to escalate costs from the initial (base) period (first quarter 1994) forward to any quarter in the future. To date, final indexes have been calculated (and are presented at the end of this article) for the second, third, and fourth quarters of 1994, and first quarter 1995; preliminary indexes are provided for second quarter 1995. Quarterly updates of these cost indexes will be computed as soon as the required input data become available. To date, no other set of cost indexes has been developed formore » such a wide array of pollution-control devices.« less

Blast furnaces make way for new steel technology

Abstract: Increasingly stringent environmental regulations, aging production units, and a competitive market are forcing iron and steelmakers to improve the environmental performance and cost efficiencies of their processes. The traditional integrated steel unit isn`t obsolete -- yet. Blast furnaces will be around for at least another 15 years. However, traditional technology is in for some changes, and stepped up rivalry from electric arc furnace minimills and ironmaking processes that use gas or coal. The paper discusses direct iron making processes, the DRI-minimill connection, the iron carbide process, and reclaiming iron from waste.

Activated carbon gets revved up

Abstract: When it comes to adsorption, few products can match the low cost and efficient performance of activated carbon. That`s why the material is so widely used for wastewater treatment. But with processors looking for economical ways to achieve environmental compliance in other operations, the market s taking off in different directions, wit much attention focused on air purification, process water treatment and solvent recovery. It is the opportunity that manufacturers and marketers of activated carbon have been waiting for. All revved up, they are generating new products and regenerating spent carbon, and rounding out their offerings with equipment and technical service. The article discusses new products and applications, increasing regeneration capacity, and competition in the activated carbon industry.

On the level. Measuring liquid level : a guide for CPI users

Abstract: A brief selection guide discusses the pros and cons of the various types of systems for measuring liquid level

Installing liquid-ring vacuum pumps

Abstract: As with any pump, care should be taken in unpacking the pump so as not to damage or misalign the assembly. For pump and motor units mounted on a baseplate, the unit should be lifted by the base only. Slings or hooks should not be attached to the pump or motor, since this can cause misalignment. Also, the pump should not be run until it is properly installed, nor should it be run without a sealing liquid.

Beware of condenser fouling

Abstract: Many chemical process plants generate steam for power production and process use. Recovering this steam as condensate, and returning it to the boiler, is an economical way to recycle heat. This is usually done in a watercooled, steam-surface condenser located at the exhaust of a turbine. Poor performance of such a condenser -- which is really a large heat exchanger -- can significantly decrease a plant`s heat-recycling efficiency. The most-common causes of condenser inefficiency are: microbiological growth on the water side, scale formation on the water side, tube pluggage by debris and air in-leakage on the steam side. These problems can cost a plant dearly. Well-planned treatment programs to combat these causes, however, pay for themselves many times over. The paper discusses these four types of fouling and solutions to their mitigation.

Online testing assures integrity of sensors.II

Abstract: We present an overview of online techniques for testing the response time of resistance temperature detectors (RTDs), thermocouples and pressure transmitters. Online testing at process conditions provides information about the dynamic performance of sensors, such as the degradation that occurs over long operating periods