Iazstru entation for and Oil e f i n e r i e s
owes
T h e use of a product quality analyzer for oil processing cannot be justified statistically. Oil refineries, which are basically constant throughput, long running units, making a blendable liquid product, have for this reason not generally adopted such instruments because almost ideal conditions can be obtained with their present lesstroublesome instrumentation. Boilerhouses have the instrumentation know-how and can calculate stack losses accurately to justify the cost of oxygen or carbon dioxide recorder controllers t o replace the air flow-steam flow combustion control element, but this instrumentation also is, in general, being ignored because steam flow-air flow measurement is fast and accurate and is preferred to the direct measurement of oxygen with its inherent sampling and measuring lags. Solid product manufacturers, who are unable to blend or rerun spoilage, therefore, are the logical potential market for specialized product quality instrumentation.
J. A. Pellettere Gulf Oil Corp., Pittsburgh 38,Pa.
T
real test or proof of the need for high priced specialized analyzers and their helper instruments to reduce time lags is the amount of rerunning necessary in the operating unit to obtain a salable product and the possibilities for increased capacity. Boilerhouses and refineries are representative of industries which have not generally adopted “superinstrumentation.” The boilerhouse probably could justify the costs of specialized instrumentation, but prefer its present less-troublesome controls.
control stack losses. For normal operation the steam meter is used as a measurement of fuel, and air is ratioed to steam flow. The steam meter is used because sampling time and difficulty with keeping gas analyzer filters clean lead to lags of a high order and to lack of dependability in a gas analyzer’s performance. The modern one-drum boiler is exceedingly fast, and a control circuit built around a slow-response gas analyzer is not practicable as long as steam meters are available and perform so well; the steam meter has no inherent lags and is very dependabIe.
Boilerhouse Instrumentation Quality control in the modern boilerhouse involves little, if any, instrumentation. Efficiency of steam generation is reflected in the percentages of carbon dioxide, carbon monoxide, and oxygen in the stack gases. High values of excess oxygen and low percentages of carbon dioxide represent a definite loss in fuel energy, showing up as wasted heat in the stack. These losses can be calculated readily and are conclusive proof as to the efficiency of operation of the unit. Flue gases with low carbon dioxide readings and the presence of carbon monoxide represent an irretrievable loss since the boilerhouse operator is unable to reprocess the flue gas by rerunning it through the fuel tanks. Boilerhouse control, however, is more complex than refinery control, for example, primarily because the boilerhoude does not maintain a fixed load but generates steam in accordance with demand as measured by the steam header pressure: There are three or four automatic functions being controlled simultaneously -namely, ratio of air to fuel, in order to keep the carbon dioxide in the flue gas a t a high percentage; fueling of the boiler in accordance with steam header pressure, in order to meet the steam demand; admission of water to the drum, in order to maintain a level under varying load or demand; and operation of the fans or the air input in such a manner as to control the furnace draft a t slightly less than atmospheric pressure, in order that fires do not leave the furnace and back into the room. These multifunctioning controls have been developed to an advanced stage by designers of control equipment. Thus, a combustion engineer can determine quite accurately the amount of fuel lost because of poor combustion. Since the fuel loss cannot be reclaimed, the cost of automatic boilers can usually be justified on the basis of improved efficiency. An oxygen controller in a cascaded instrument circuit has been developed especially to reduce sampling time lag in boilerhouses; however, boilerhouses, in general, are not using such analyzers to
Refinery Instrumentation Oil refineries are basically liquid product plants of large capacity, operating for long periods a t constant load. Designers of refining equipment today endeavor to design for one year’s operation a t full capacity and expect a cycle in excess of 90% on stream time. Except during the first day when the unit is being brought on stream, capacity and performance are at a constant rate, 11 hich is usually that of maximum design. In general, the products made in such a unit are constantly under laboratory control. The laboratory checks running stream quality, running tank quality, and quality of mateiial loaded to transport vessels such as boats, tank cars, tiucks, or pipelines. If “superinstrumentation” were utilized in an oil refinery to control all points of quality and the laboratory x-eie eliminated, the product cost would not be lowered materially. Refiners also have an advantage in making a liquid product which can be blended for small discrepancies to final product specifications. The instrument panel of a modern airplane represents the simplest form of concentrated or centralized control house, wherein control consists of the operator making a corrpction by hand to restore the indicator to its normal position. In the automobile industry mass production is based on the conveyor line or belt system by means of which the work or product is passed by the mechanic or operator in such a manner that he performs his function by standing in one place. The belt with the work is the mobile unit. Refineries differ from both the airplane and the conveyor line in that production lines consist of towers, heaters, pumps, and coolers. All control data are transmitted to indicators in ,a control house; however, in the refinery the control house is really an automatic observation post which not only collects the data but also sets up the action necessary to keep these values at control
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1951
point or desired value for operation, making use of standard instruments and control laboratory. This is basic as it is important to be aware of all operating conditions at all times in order that the unit run a t full capacity continuously and produce products of good quality. Product quality is checked by the control laboratory in some cases once every 4 hours and in most cases once a shift. Under these circumstances, any attempt to get more product through the unit is unavailing.
Conclusions In manufacturing a solid product, actual losses can be determined from inventory, and these are true losses because they are not rerunable. Annual losses can be computed and an investment to prevent such losses can be justified even if the investment requires specialized analyzers with inherent time lags and helper instruments (commonly known as cascaded instrumentation) to reduce the lag. In boilerhouses boiler performance charts provide the data for calculating losses from carbon dioxide or oxygen measurements taken periodically either by hand or by
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instrument. These losses are not recoverable-here, too, definite expenditures can be justified for specialized instrumentation to avoid losses due to human fatigue and error in poor operation. The refinery that produces liquid products, however, cannot set up these clear-cut calculations of losses. On the basis that the cost of rerun on a liquid process unit is essentially loss in capacity, plus the extra fuel and labor required for the second processing, modern refineries eannot establish losses when units are running continually a t full capacity. When superanalyzers are available and suitable for oil refinery stills, refiners will not hesitate to use the instrumentation required to justify the economics involved. Refiners are considered leaders in the use of controls for continuous operation, and future usage of specialized instrumentation is not excluded on any basis. However, a t the present time, manufacturers of continuous process liquid products have no complaint with standard instrumentation and do not agree that there is dire need of better quality measuring instrumentation-especially in refineries. RECEIVED May 1. 1951
Instrumentation in Radioactive Svsterns W
T h i s paper attempts to answer some of the questions asked on the requirements for instrumentation in radioactive systems. The basic needs for instrumentation are explained for various types of radioactive processes, such as reactors, chemical and physical separation, and metallurgical operations. The variables to be measured, their accuracy, and their response times are outlined with general rules for installation. The need for reliability in primary detectors is explained. Protection of pereonne1 from radiation is described to show the strong effect of this necessary function on instrument maintenance costs. An effort is made to summarize the progress of instrumentation in radioactive systems and to speculate on the progress to be made.
C. A. Hansen, Jr. Knolls AtomZc Power Laboratorg, Schnectadw, N . Y.
R
ADIOACTIVE systemsinclude nuclear, chemical,and physical processes. In each general field the operations may be quite diverse in character and present different problems with respect to instrumentation, In order to instrument a process, it must be defined and the conditions under which a variable is to be measured must be known. Prior to attempting to establish some general rules for instrumentation in radioactive systems, it would be worthwhile to outline in a general manner some of the individual processes under the broad headings of nuclear, chemical, and physical operations.
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Nuclear The nuclear reactor or “pile” represents the best example of the nuclear processes. There are a number of factors necessary to describe a reactor. The following very incomplete tabulation serves as an illustration: 1. Function Plutonium production Power ExDeriment 2. Neution spectrum Thermal Intermediate Fast 3. Moderator Graphite Water Heavy water
4. Fuel
5.
6.
Natural uranium Enriched uranium Plutonium Coolants Water Air or gas Liquid metals Coolant system 0 en Cfosed cycle
The factors having primary effect on the instrumentation are:
1. Neutron flux density 2. Coolant and coolant system 3. Operating temperature 4. Internal reactor arrangement, in so far as it limits available space All reactors operating a t a reasonably high power level have the common problem of securing primary detectors that will withstand radiation without deterioration. The variables to be measured are essentially the same for all reactors: 1. Neutron flux 2. Rod or control element position 3. Temperature 4. Flow 5. Pressure Additional variables may require measurement depending on reactor design.
Chemical The chemical processes are reduction of fissionable material to elemental or compound forms for use in other operations; and separation of plutonium and other elements from irradiated materials. The preparation of fissionable materials does not as a rule in-
