Process plant scale

Approximately 50—55% of the product from a coal-tar refinery is pitch and another 30% is creosote. The remaining 15—20% is the chemical oil, about half of which is naphthalene. Creosote is used as a feedstock for production of carbon black and as a wood preservative. Because of modifications to modem coking processes, tar acids such as phenol and cresyUc acids are contained in coal tar in lower quantity than in the past. To achieve economies of scale, these tar acids are removed from cmde coal tar with a caustic wash and sent to a central processing plant where materials from a number of refiners are combined for recovery. 

The alkalized zinc oxide—chromia process developed by SEHT was tested on a commercial scale between 1982 and 1987 in a renovated high pressure methanol synthesis plant in Italy. This plant produced 15,000 t/yr of methanol containing approximately 30% higher alcohols. A demonstration plant for the lEP copper—cobalt oxide process was built in China with a capacity of 670 t/yr, but other higher alcohol synthesis processes have been tested only at bench or pilot-plant scale (23). 

A modification of the conventional soy protein isolate process has been investigated on a small pilot-plant scale. It is based on the absorption of water from the aqueous protein after extraction at pH 8.5 using temperature-sensitive polyisopyropylacrylamide gels, followed by spray drying to give a 96% protein isolate (111). 

A considerable quantity of oil can be extracted from waste material from shelling and processing plants, eg, the inedible kernels rejected during shelling and fragments of kernels recovered from shells. About 300 t of pecan oil and 300—600 t of English walnut oil are produced aimuaHy from such sources. The oil is refined and used for edible purposes or for the production of soap the cake is used in animal feeds (see Feeds and feed additives). Fmit-pit oils, which closely resemble and are often substituted for almond oil, are produced on a large scale for cosmetic and pharmaceutical purposes (143). For instance, leaves, bark, and pericarp of walnut may be used to manufacture vitamin C, medicines, dyes and tannin materials (144). 

A circulating fluidized-bed boiler, using raw shale oil as a feedstock, is being used to supply process heat for the phosphate operations and to operate a 100-MW power plant. Scale-up in the 1990s should increase the electric power generation to 1000 MW (71). 

The first commercial plant to use CYANEX 272 became operational in 1985. An additional three plants were constmcted between 1985 and 1989. Of the four, one is in South America and three in Europe. An additional three plants have been built two in Europe (1994) and one in North America (1995). Approximately 50% of the Western world s cobalt is processed using CYANEX 272. Both high purity salts and electrolytic cobalt metal are recovered from solutions ranging in composition from 30 g/L each of cobalt and nickel to 0.2 g/L Co, 95 g/L Ni Operating companies usually regard use of CYANEX 272 as confidential for competitive reasons and identities cannot be disclosed. CYANEX 272 is being evaluated on the pilot-plant scale in many additional projects involving the recovery of cobalt and other metals. 

Process plant design has come a long way from the early 1930s when process designers used the rule-of-thumb that a process faciUty could not be scaled-up more than 10-fold (2). American Oil s Ultracracking unit (Texas City, Texas) for example, was designed from data from a small pilot plant with a scale-up factor of 80,000 (3). 

Pilot-plant start-up is different from principal process plant start because of the smaller scale of the unit, smaller resources committed, lack of advance start-up planning, and limited experience with the pilot-plant process and operation. 

Pilot plants are often more hazardous than process plants, even though they are smaller ia size, for many reasons. These iaclude a tendency to relax standard safety review procedures based on the small scale, exceptionally qualified personnel iavolved, and the experimental nature of the research operations the lack of estabhshed operational practice and experience lack of information regarding new materials or processes and lack of effective automatic iatedocks due to the frequendy changing nature of pilot-plant operations, the desire for wide latitude in operating conditions, and the lack of hill-time maintenance personnel. 

Tantalum Compounds. Potassium heptafluorotantalate [16924-00-8] K TaF, is the most important tantalum compound produced at plant scale. This compound is used in large quantities for tantalum metal production. The fluorotantalate is prepared by adding potassium salts such as KCl and KF to the hot aqueous tantalum solution produced by the solvent extraction process. The mixture is then allowed to cool under strictiy controlled conditions to get a crystalline mass having a reproducible particle size distribution. To prevent the formation of oxyfluorides, it is necessary to start with reaction mixtures having an excess of about 5% HF on a wt/wt basis. The acid is added directiy to the reaction mixture or together with the aqueous solution of the potassium compound. Potassium heptafluorotantalate is produced either in a batch process where the quantity of output is about 300—500 kg K TaFy, or by a continuously operated process (28). 

Esterification is generally carried out by refluxing the reaction mixture until the carboxyHc acid has reacted with the alcohol and the water has been spHt off. The water or the ester is removed from the equiUbrium by distillation. The choice of the esterification process to obtain a maximum yield is dependent on many factors, ie, no single process has universal appHcabiUty. Although extensive preparative techniques have been reviewed elsewhere (7,68), the methods given ia this section are representative of both laboratory and plant-scale techniques used ia batch esterifications. 

The results of the Flixborough investigation made it clear that the large inventory of flammable material in the process plant contributed to the scale of the disaster. It was concluded that limitations of inventory should be taken as specific design objectives in major hazard installations. It should be noted, however, that reduction of inventoiy may require more frequent and smaller shipments and improved management. 

In certain cases, it is necessary to choose materials for equipment to be used in a process developed in the laboratory and not yet in operation on a plant scale. Under such circumstances, it is obviously impossible to make plant tests. A good procedure in such cases is to construct a pilot plant, using either the cheapest materials available or some other materials selected on the basis of past experience or of laboratory tests. While the pilot plant is being operated to check on the process itself, specimens can be exposed in the operating equipment as a guide to the choice of materials for the large-scale plant or as a means of confirming the suitability of the materials chosen for the pilot plant. 

Ion probes. Determining the level of ions in solution also helps to control corrosion. An increase in concentration of specific ions can contribute to scale formation, which can lead to a corrosion-related failure. Ion-selective elec trode measurements can be included, just as pH measurements can, along with other more typical corrosion measurements. Especially in a complete monitoring system, this can add information about the effect of these ions on the material of interest at the process plant conditions. 

Experimental analysis involves the use of thermal hazard analysis tests to verify the results of screening as well as to identify reaction rates and kinetics. The goal of this level of testing is to provide additional information by which the materials and processes may be characterized. The decision on the type of experimental analysis that should be undertaken is dependent on a number of factors, including perceived hazard, planned pilot plant scale, sample availability, regulations, equipment availability, etc. 

Tuma, L. and C. Bagner 1998. Assurance of Safe Pilot Plant Scale-Up of Chemical Processes, in (G. A. Melhem and H. G. Fisher, eds.). International Symposium on Runaway Reactions, Pressure Relief Design, and Effluent Handling, American Institute of Chemical Engineers, New York. 

Laboratories Listed toxic chemicals that are manufactured, processed, or otherwise used in laboratory activities at a covered facility under the direct supervision of a technically qualified individual do not have to be factored into the threshold and release calculations. However, pilot plant scale and specialty chemical production do not qualify for this laboratory activities exemption. 

There are numerous stages of activities that must be conducted before an actual process, plant or even small-scale pilot system reaches its operational... 

Chemical reaction hazards must be considered in assessing whether a process can be operated safely on the manufacturing scale. Furthermore, the effect of scale-up is particularly important. A reaction, which is innocuous on the laboratory or pilot plant scale, can be disastrous in a full-scale manufacturing plant. For example, the heat release from a highly exothermic process, such as the reduction of an aromatic nitro compound, can be easily controlled in laboratory glassware. Flowever,... 

Process investigation manager responsible for investigating technical problems and for transferring laboratory results to plant-scale operations. 

In many cases, two identical reaction systems (e.g., a pilot plant scale and a full-scale commercial plant) exhibit different performances. This difference in performance may result from different flow patterns in the reactors, kinetics of the process, catalyst performance, and other extraneous factors. 

For a new process plant, calculations can be carried out using the heat release and plume flow rate equations outlined in Table 13.16 from a paper by Bender. For the theory to he valid, the hood must he more than two source diameters (or widths for line sources) above the source, and the temperature difference must be less than 110 °C. Experimental results have also been obtained for the case of hood plume eccentricity. These results account for cross drafts which occur within most industrial buildings. The physical and chemical characteristics of the fume and the fume loadings are obtained from published or available data of similar installations or established through laboratory or pilot-plant scale tests. - If exhaust volume requirements must he established accurately, small scale modeling can he used to augment and calibrate the analytical approach. 

A centrifuge on a crystallization process plant is to be scaled down for tests. If the plant centrifuge is 1.0 m diameter and rotates at 25 Hz at what speed should a 100 mm laboratory centrifuge run if it is to duplicate plant conditions ... 

After many years of improvements in technical safety methods and process design, many orgaruzations have found that accident rates, process plant losses and profitability have reached a plateau beyond which further improvements seem impossible to achieve. Another finding is that even in orgarriza-tions with good general safety records, occasional large scale disasters occur which shake public confidence in the chemical process industry. The common... 

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