Supply pressure

Schemes to control the outlet temperature of a process furnace by adjusting the fuel gas flow are shown in Figure 13. In the scheme without cascade control (Fig. 13a), if a disturbance has occurred in the fuel gas supply pressure, a disturbance occurs in the fuel gas flow rate, hence, in the energy transferred to the process fluid and eventually to the process fluid furnace outlet temperature. At that point, the outlet temperature controller senses the deviation from setpoint and adjusts the valve in the fuel gas line. In the meantime, other disturbances may have occurred in the fuel gas pressure, etc. In the cascade control strategy (Fig. 13b), when the fuel gas pressure is disturbed, it causes the fuel gas flow rate to be disturbed. The secondary controller, ie, the fuel gas flow controller, immediately senses the deviation and adjusts the valve in the fuel gas line to maintain the set fuel gas rate. If the fuel gas flow controller is well tuned, the furnace outlet temperature experiences only a small disturbance owing to a fuel gas supply pressure disturbance.

Grade Purity, min vol % Supply pressure, MPa Cylinder price, / cylinder Gas price, /m ... 

Most of the commercial gas—air premixed burners are basically laminar-dow Bunsen burners and operate at atmospheric pressure. This means that the primary air is induced from the atmosphere by the fuel dow with which it mixes in the burner passage leading to the burner ports, where the mixture is ignited and the dame stabilized. The induced air dow is determined by the fuel dow through momentum exchange and by the position of a shutter or throtde at the air inlet. Hence, the air dow is a function of the fuel velocity as it issues from the orifice or nozzle, or of the fuel supply pressure at the orifice. With a fixed fuel dow rate, the equivalence ratio is adjusted by the shutter, and the resulting induced air dow also determines the total mixture dow rate. 

If the substitute fuel is of the same general type, eg, propane for methane, the problem reduces to control of the primary equivalence ratio. For nonaspiring burners, ie, those in which the air and fuel suppHes are essentially independent, it is further reduced to control of the fuel dow, since the air dow usually constitutes most of the mass dow and this is fixed. For a given fuel supply pressure and fixed dow resistance of the feed system, the volume dow rate of the fuel is inversely proportional to. ypJ. The same total heat input rate or enthalpy dow to the dame simply requires satisfactory reproduction of the product of the lower heating value of the fuel and its dow rate, so that WI = l- / remains the same. WI is the Wobbe Index of the fuel gas, and... 

A 1990 study by American Cyanamid Co. demonstrated that the reaction cycle depends also on the supply pressure of the gaseous nitrogen. The 3-d reaction cycle at the normal 75 Pa (0.3-ia. water) pressure can be reduced to 2.4 d usiag the N2 gas pressure at 2 kPa (8-ia. water) iato the oveas (19). 

Trip Valves The trip valve is part of a system that is used where a specific valve action (i.e., fail up, Fail down, or lock in last position) is required when pneumatic supply pressure to the control valve falls befow a preset level. Trip systems are used primarily on springless piston ac tuators requiring fail-open or fail-closed acrion. An air storage or Volume tank and a check v ve are used with the trip valve to provide power to stroke the valve when supply pressure is lost. Trip valves are designed with hysteresis around the trip point to avoid instabihty when the trip pressure and the reset pressure settings are too close to the same value. 

Another purpose of inerting is to control oxygen concentrations where process materials are subject to peroxide formation or oxidation to form unstable compounds (acetylides, etc.) or where materials in the process are degraded by atmospheric oxygen. An inert gas supply of sufficient capacity must be ensured. The supply pressure must be monitored continuously. 

Design vessel to accommodate maximum supply pressure... 

High or low fuel gas pressure ean have a dramatic effect on the operation of a firetube heater. Burners are typically rated as heat output at a specified fuel pressure. A significantly lower pressure means inadequate heat release. Significantly higher pressure causes overfiring and over heating. The most common causes of a fuel gas pressure problem are the failure of a pressure regulator or an unacceptably low supply pressure. 

Ensure that the rated maximum inlet pressure of the regulator is not less than the eylinder supply pressure. (Eor eylinder pressures up to 200 bar, pressure regulators should eomply with BS 5741. Eor higher eylinder pressures eheek with the manufaeturer that the pressure regulator has been shown to be suitable by appropriate testing.)... 

Volumetric or gravimetric feeders may be used, but volumetric feeders are usually selected only for installations where comparatively low feed rates are required. Dilution does not appear to be important, therefore, control of the amount of water used in the feeding operation is not considered necessary. Inexpensive hydraulic jet agitation may be furnished in the wetting chamber of the feeder as an alternative to mechanical agitation. The jets should be sized for the available water supply pressure to obtain proper mixing. 

Steam Turbine - A PR valve is required on the steam inlet to any steam turbine if the maximum steam supply pressure is greater than the design pressure of the casing inlet. The PR valve should be set at the casing inlet design pressure and sized such that overpressure of the casing is prevented, under conditions of wide open steam supply and normal exhaust flow. 

Can the supply pressure of raw materials be limited to less than the working pressure of the vessels they are delivered to ... 

The nitrogen supply used to purge the metal cabinet was also used to blow out the dryers. When the iiiirngcn supply pressure fell occasionally, solvent from the dryers entered ihrtmgh leaking valves into the nitrogen supply line,, ind into the metal cabinet. Low nitrogen pressure allowed air diffusion into the cabinet. 

Should start automatically when supply pressure falls below a certain level. 

WHEN DISCHARGING TO PRESSURES HIGHER THAN ATMOSPHERIC. MULTIPLY VELOCITY TO ATMOSPHERE BY FACTOR CORRESPONDING TO SUPPLY PRESSURE AND RECEIVER PRESSURE. 

Normal supply pressure to industrial and commercial users is 21 mbar. Allowing for pressure losses in the system, at least 17.5 mbar should be available at the point of use. Higher pressures can often be supplied by agreement where available. There may be process advantages in having a higher pressure. 

Constant-pressure governors are required at various stages of the gas supply within the user s premises from the first pressure reduction from distribution pressure to supply pressure at the meter installation to the appliance governor. The complexity and design of the governor installation depends on pressure, throughput, duty, etc. In addition to governors, pressure-relief, slam-shut and non-return valves may be relevant in some installations. 

Slam-shut valves are usually set to operate under conditions of high downstream pressure. They can be used for low pressures, and combined high and low. Although they normally protect the supply pressure to premises using gas, slam-shut valves are sometimes used on process plant. 

The Wobbe number of gas is defined as The heat release when a gas is burned at a constant gas supply pressure . It is represented by ... 

Distribution systems can be operated at pressures up to 7 bar but it is practice to operate at as low a pressure as is consistent with supplying users with the agreed supply pressure, which is 21 mbar at the meter inlet in many cases. Pressure reduction takes place at take-offs from the transmission system, at district governor installations serving a large number of users within a geographical area and, for many larger users, at the users premises. 

The effect of the air is to depress the vapor dew point temperature. A further advantage is that the physical properties of the gas can be made to simulate another gas, e.g. natural gas or manufactured town gas. Such a simulated gas will produce the same heat release through a burner if the supply pressure is the same. This is characterized by a term known as the Wobbe number W) ... 

The steam flow through a valve at critical pressure drop when P2, the downstream pressure, is 0.58 times PI, the supply pressure, or P2/P1 = 0.58, is given very closely by W = 2KvP, where W = steam flow (kg/h), Kv = flow coefficient and PI = supply pressure (bar). In the USA, W = 1.5Cr>Pl, where W = steam flow (pph), Cv = flow coefficient and PI = supply pressure (psia). The factors... 

Pressure reducing valves provide a steady pressure into a part of the system that operates at a pressure lower that normal system pressure. A reducing valve can normally be set for any desired downstream pressure within its design limits. Once the valve is set, the reduced pressure will be maintained regardless of changes in the supply pressure and system load variations. 

A two-stage centrifugal compressor will be used for both duties. Take the polytropic efficiency for both compressors as 70 per cent. The hydrogen supply pressure is 120 kN/m2 and the temperature 25 °C. The hydrogen chloride is cooled to 50 °C after leaving the burner. Assume that the compressor intercooler cools the gas to 50 °C, for both duties. 

Steam, and other vapour heating systems, are intrinsically safe as the temperature cannot exceed the saturation temperature at the supply pressure. Other heating systems rely on control of the heating rate to limit the maximum process temperature. Electrical heating systems can be particularly hazardous. 

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