Start-up Pressure

Small capacity pumps commonly referred to as "jockey" pumps are provided on a firewater system to compensate for small leakages and incidental usage without the main pump(s) startup. They are set to start 0.70 to 1.05 kg/sq. cm. (10 to 15 psi) above the start up pressure of main firewater pumps. In some cases a cross-over from the utility water system can be used in place of a jockey pump, however a check valve is installed to prevent drain down of the firewater by the utility water system. Jockey pumps do not require the... 

For thixotropic slurries, methods are used to predict start-up pressure after a shutdown of the pipeline, and the time required to clean the conduit of gelled material before resuming pumping. 

The start-up pressure for pumping a Bingham plastic is expressed in terms of the true yield stress ... 

The start-up pressure per unit length is obtained by dividing Equation 5-1 by the... 

A slurry consists of a clay and water mixture. It is tested and classified as a Bingham mixture with a yield stress of 17 Pa. The pipe inner diameter is 63 mm. The pipe length is 6500 m. Determine the start-up pressure, ignoring any static head. 

The start-up pressures for thixotropic slurries may be quite high, particularly when these slurries coagulate into gels inside the pipeline. During an initial of period of time, gels must be expelled from the pipeline. Crude oils, fuel oils, bentonite clay, and drilling... 

Start up pressure to pump a non-Newtonian slurry Flow rate... 

Regarding product characteristics, European specifications were established in 1992. They concern mainly the motor octane number (MON) that limits the olefin content and which should be higher than 89, and the vapor pressure, tied to the C3/C4 ratio which should be less than 1550 mbar at 40°C (ISO 4256). On the other hand, to ensure easy vehicle start-ups, a minimum vapor pressure for winter has been set which is different for each country and depends on climatic conditions. Four classes. A, B, C, and D, are thus defined in Europe with a minimum vapor pressure of 250 mbar, respectively, at -10°C (A), -5 C (B), 0°C (C) and -t-10°C (Z)). France has chosen class A. 

Thermal Stresses. When the wak of a cylindrical pressure vessel is subjected to a temperature gradient, every part expands in accordance with the thermal coefficient of linear expansion of the steel. Those parts of the cylinder at a lower temperature resist the expansion of those parts at a higher temperature, so setting up thermal stresses. To estimate the transient thermal stresses which arise during start-up or shutdown of continuous processes or as a result of process intermptions, it is necessary to know the temperature across the wak thickness as a function of radius and time. Techniques for evaluating transient thermal stresses are available (59) but here only steady-state thermal stresses are considered. The steady-state thermal stresses in the radial, tangential, and axial directions at a point sufficiently far away from the ends of the cylinder for there to be no end effects are as fokows ... 

Wet air oxidation is based on a Hquid-phase oxidation between the organic material in the wastewater and oxygen suppHed by compressed air. The reaction takes place flamelessly in an enclosed vessel which is pressurized and at a high temperature, typically 13.79 x 10 Pa and 575°C. The system temperature, initiated by a start-up boiler, is maintained through auto thermal combustion of organics once the reaction starts. 

A minimum volatihty is frequently specified to assure adequate vaporization under low temperature conditions. It can be defined either by a vapor pressure measurement or by initial distillation temperature limits. Vaporization promotes engine start-up. Fuel vapor pressure assumes an important role particularly at low temperature. For example, if fuel has cooled to —40°C, as at arctic bases, the amount of vapor produced is well below the lean flammabihty limit. In this case a spark igniter must vaporize enough fuel droplets to initiate combustion. Start-up under the extreme temperature conditions of the arctic is a major constraint in converting the Air Force from volatile JP-4 to kerosene-type JP-8, the military counterpart of commercial Jet Al. 

In most existing styrene processes, the catalyst is loaded into large, radial flow reactors, which are operated adiabaticaHy at low pressure and temperatures near 600°C. Heat is suppHed by superheated steam. During start-up, dehydrogenation begins slowly and accelerates as the Fe (HI) is reduced to Fe (II,III). The catalyst, which was red in color when fresh, turns to the characteristic black color of Fe O. ... 

Explosibility and Fire Control. As in the case of many other reactive chemicals, the fire and explosion hazards of ethylene oxide are system-dependent. Each system should be evaluated for its particular hazards including start-up, shut-down, and failure modes. Storage of more than a threshold quantity of 5000 lb (- 2300 kg) of the material makes ethylene oxide subject to the provisions of OSHA 29 CER 1910 for "Highly Hazardous Chemicals." Table 15 summarizes relevant fire and explosion data for ethylene oxide, which are at standard temperature and pressure (STP) conditions except where otherwise noted. 

Roller conveyors are quite frequently powered, the simplest method being use of a pressure belt in contact with the lower surface of the rolls. A special ripple belt with raised pads is capable of starting up the load but does not build up excessive blocked pressure if the line fills up. Other similar drives are available, with varying degrees of control over the applied power. Most expensive of the powered roller units are those in which each roll is equipped with V-belt or chain drives. Pusher bars suspended from overhead chain conveyors may also be used to move containers along a roller hne. 

Once fundamental data have been obtained, the goal is to develop a mathematical model of the process and to utilize it to explore such possibilities as produc t selectivity, start-up and shut-down behavior, vessel configuration, temperature, pressure, and conversion profiles, and so on. 

Basic process control system (BPCS) loops are needed to control operating parameters like reactor temperature and pressure. This involves monitoring and manipulation of process variables. The batch process, however, is discontinuous. This adds a new dimension to batch control because of frequent start-ups and shutdowns. During these transient states, control-tuning parameters such as controller gain may have to be adjusted for optimum dynamic response. 

Onee ease starts to pressure up (50 psi or better), switeh No. 1 lube oil pump to manual. 

Starting up and shutting down the expander must not adversely affect tlie differential pressure between tlie reactor and tlie regenerator. 

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