Counterflow cooling towers in many large petrochemical plants, refineries and power plants throughout the world were built 10 to 15 years ago and still use heat transfer techniques that are over 50 years old. When cooling towers were first developed, the concept was to break the water into small droplets and have them fall downward through wood splash bars. The bars were of a sufficient height to have the entering hot water droplets cooled adequately at the cold water basin level to approximately the required cold water temperature. However, there was still some residual heat left within the water droplets. Over the years improvements in the mechanical equipment and structural designs were made, but the basic water splash droplet concept continued. As water flow requirements increased, so did the height and size of the cooling towers to accommodate these new requirements. Listed are the various internal elements of the modern counterflow cooling tower and their engineered state-of-the-art upgrading capabilities compared to the old fashioned methods.
One of the many significant factors influencing machinery reliability in process plants is alignment accuracy. When driven process machines operate in misaligned condition with respect to their drivers, equipment bearings are exposed to additional loads. Vibration severity may increase, bearings will be more highly loaded and equipment life expectancy will diminish. This paper reports on the use of laser optics for on-stream alignment verification.
High temperature gas piping systems in refineries and petrochemical complexes incorporate a variety of components in addition to the piping. These components involve a variety of materials other than basic piping materials. Also, the various components frequently operate at temperatures below the process temperature. Nevertheless, system designers frequently write common hydrostatic test pressure specifications for the entire system regardless of these differences in piping and component materials and operating temperatures. Generally, the material used as the basis for this common system hydrostatic test pressure calculation is the piping material. This is the material of largest usage and often the material with the lowest allowable strength at the design temperature. This paper discusses how to improve piping and expansion joint design.
The proposed OSHA regulations for process safety management of highly hazardous chemicals (29 CFR 1910.119) have set the stage for a federally mandated process safety management (PSM) program to be implemented. As with any such mandate, there will always be some concern as to whether the program is manageable, workable for the parties who are charged with implementation, comprehensive, and cost effective. While the manageability and cost effectiveness of any such program will depend upon circumstantial factors, industry has begun to agree upon elements that would make up a comprehensive PSM program. This paper discusses how an industry based program is being implemented.
The U.S. Environmental Protection Agency (EPA) is in the process of amending a variety of regulations that will require better ways to look at emissions, as well as adding regulations for monitoring additional pollutants. And changes in the newly revised Clean Air Act (CAA) are now effective. These changes require monitoring to check the progress in reaching attainment targets for control of ozone. EPA aims to see increased monitoring provisions in urban areas for air toxics and other chemicals. Another example of increased monitoring regulations is the Safe Drinking Water Act Amendments of 1986, now effective. These require monitoring of over 100 drinking water constituents. The authors discuss how these examples point to the trend of increased monitoring of air, water and process streams, which will place a stronger demand on monitoring equipment.
Laboratory testing and evaluation of fresh FCC catalysts involves two steps - a deactivation step and a catalytic step. Much attention has historically been given to improved methods for laboratory catalytic performance evaluation in microactivity and pilot plant testing, particularly with respect to simulating the reaction conditions of a commercial FCC riser. Proper simulation of the deactivation mechanisms which occur commercially in a laboratory deactivation procedure is equally important. The measurement of steamed catalyst properties such as zeolite unit cell size, surface area, etc., can be used to guide in selection of steaming conditions which target typical equilibrium properties for a particular catalyst. Steamed properties provide a much better correspondence with catalyst performance than fresh properties. Some examples are discussed which illustrate this point. Because the nature of FCC unit operation dictates that a small fraction of the catalyst inventory be replaced with fresh catalyst on a continual basis, a distribution of properties reflecting the age distribution will exist in any equilibrium sample. A deactivation model is presented which combines catalyst and unit parameters to generate predicted equilibrium catalyst property distributions.
The increasing role of refinery product quality control is significant. Driven not only for meeting product specification and economic goals, refiners must also satisfy new purchaser demands. That is, the emphasis to monitor product quality on-line in an accurate, timely manner is greater now than ever, due largely to the expanding use of statistical methods (SQC/SPC) in analyzing and manipulating process operation. Consequently, the need for reliable composition control is essential in maintaining refinery prosperity. Process gas chromatographs are frequently used to monitor the performance of distillation, absorption and stripping towers by providing near-real-time stream composition, particular component concentration, or calculated parameter (Rvp, Btu content, etc.) information. This paper reports that appreciably greater benefit can be achieved when process gas chromatographs (or GCs) provide on-line feedback data to process control schemes.
There are numerous methods for evaluating process energy efficiency. They involve representations of the process system to varying degrees of complexity in the search for lost Btus. Many of these methods often try to maximize heat recovery for a single process while ignoring effects in downstream units. Thus, decreased energy use in one unit may result in increased energy use in another. Several other methods attempt detailed studies to find savings without first establishing a target energy consumption against which to measure progress. A method exists which can be used to easily establish targets and compare current operation to these targets. Process units do not need to be considered in isolation and effects of heat recovery on subsequent units can be accounted for. Included in this method is a systematic analysis which allows quick identification of specific areas where energy efficiency improvements are most likely to be realized. This results in subsequent evaluations being focussed on items with the highest heat recovery potential.
Optimum plant operation can often be achieved by means of constraint control instead of model- based on-line optimization. This is because optimum operation is seldom at the top of the hill but usually at the intersection of constraints. This article describes the development of a constraint control system for a plant producing ethylbenzene (EB) by the Mobil/Badger Ethylbenzene Process. Plant optimization can be defined as the maximization of a profit function describing the economics of the plant. This function contains terms with product values, feedstock prices and operational costs. Maximization of the profit function can be obtained by varying relevant degrees of freedom in the plant, such as a column operating pressure or a reactor temperature. These degrees of freedom can be varied within the available operating margins of the plant.
This paper includes flow diagrams and summary descriptions for approximately 50 petrochemicals.
The explosion and fires at the Houston Chemical Complex in Pasadena, Texas, in 1989 were a worst- case scenario for Phillips Petroleum Co. The initial blast in a polyethylene unit registered a 3.0 on the Richter scale at seismographs at Rice University. There were 23 killed and more than 300 injured. The plant lost communications and much of its water system. The building housing its emergency operations center and emergency plans was wrecked in the explosion. This paper presents an assessment of the response to the explosion.
Steam plant engineers frequently have to perform energy balance calculations around the deaerator to estimate the steam required to preheat and deaerate the make-up water and condensate returns. This calculation involves solving two sets of equations, one for mass and the other for energy balance. Reference to steam tables is also necessary. However, with the help of this program written in BASIC, one can arrive at the make-up water and steam requirements quickly, without referring to steam tables. This paper shows the mass and energy balance equations for the deaerator. This paper gives the program listing. An number of condensate returns can be handled. An example illustrates the use of the program.
Saturated liquid densities for organic chemicals are given as functions of temperature using a modified Rackett equation.
For many years, automatic sampling systems have been used in determining the quality of crude oil at custody transfer points. Much has been learned regarding this aspect of measurement which has resulted in benefits to both buying and selling parties. The examination of this important procedure will help outline the requirements for successful sampling. The purpose of automatic sampling is to allow for and measure constituents in the oil which are not part of the transaction. Primarily, these include sediment and water or S and W. Thus, this conditioning procedure occurs upstream of the sampling system. A proper mixture is present when the S and W is dispersed completely across the pipe diameter, and there is a consistent droplet size in the dispersed water phase (typically less than 1,200 microns). The automatic sampling system then has a representative flowstream from which to draw each sample. There are several methods used to achieve this mixture.
Secondary containment systems (SCS) are required by EPA regulations for owners or operators of facilities using tank systems for storing or treating hazardous waste. One of the most common methods for secondary containment is to build a lined structure surrounding the primary containment tanks. This often consists of a concrete wall and flow lined with materials capable of containing the hazardous waste if the primary containment system fails. Several factors should be evaluated in the design of the lined SCS. These are reviewed in this article.
Pinch technology was originally conceived and developed as a tool for defining energy saving opportunities, particularly through improved heat exchanger network design. Subsequently, pinch technology became recognized and accepted as the preferred methodology for understanding heat and power issues in industrial processes. However, more recent research and practical experience have shown that the pinch concept can be used effectively to address a wide range of pressing process improvement issues. These include reduction of wastes and gaseous emissions, debottlenecking, reduction of capital and operating costs, improved operating flexibility and more. Thus, pinch technology has become a powerful tool to help engineers devise cost-effective ways to accomplish multiple process improvement objectives. This article describes how the pinch approach has been developed to address such wide-ranging issues. The effectiveness of the techniques is illustrated by a series of case study examples.
This article is primarily for multistage axially split pumps of over 200 hp, although the principle applies to all pumps. These pumps are frequently used for transfer of oil products (pipeline), floodwater injection systems, feedwater for boilers and in the petroleum/chemical industry. The authors argue that field performance testing of these pumps is necessary as a preventive maintenance measure.
This article deals with the simulation and optimization of a styrene plant. The mathematical model of the reactor consists of the continuity equations for each chemical component, heat balance and momentum balance equations. Both homogeneous and heterogeneous reactions are included in the model. Though all equipment in the recovery section is included, reasonable assumptions lead to a simplified recovery model which retains the accuracy of a complex model and reduces computing time. The model equations are solved numerically. The overall objective function considers both variable and fixed costs of production. The optimization is carried out using a direct search algorithm considering all plant constraints. The utilization of the model for an actual plant case is discussed.
The primary function of a flare is to dispose of toxic, corrosive or flammable vapors safely, under relief conditions, by converting them into less objectional products by combustion. Toxic limits are the greatest concentration of a poisonous substance that can be tolerated in the air for a length of time without danger. Most emergencies causing overpressure on safety relief valves can be controlled within 5 to 10 minutes, for example, by shutting down a pump or compressor. A period of 10 to 30 minutes should be sufficient to control any emergency situation short of a catastrophe. Atmospheric discharge of hydrocarbons or other flammables should be designed to avoid the formation of flammable mixtures and exposure of personnel to toxic or corrosive vapors at grade level or on elevated structures. Either elevated flares or ground flares can accomplish efficiently the discharges to atmosphere when properly designed. Proper design is based on the characteristics of waste gas, heat radiation, noise levels, smoke and atmospheric dispersion. Smokeless flares use smoke suppression systems, like stream injection, forced draft air fans, high pressure gas injection and other devices to reduce the smoking tendency of certain fuels, improving air entrainment and mixing.
Careful monitoring of the process, accurate measurement of the problem, precise metering of the treating chemicals and continuous follow-up are essential elements of a successful treatment program. This review of the ethylene production process gives an overview of the latest technology for improving efficiency and increasing run length and product quality.
