Chokes temperature

Sensors on the tree allow the control module to transmit data such as tubing head pressure, tubing head temperature, annulus pressure and production choke setting. Data from the downhole gauge is also received by the control module. With current subsea systems more and more data is being recorded and transmitted to the host facility. This allows operations staff to continuously monitor the performance of the subsea system. 

Physical Properties. Thionyl chloride [7719-09-7], SOCI2, is a colorless fuming Hquid with a choking odor. Selected physical and thermodynamic properties are Hsted in Table 6. Thionyl chloride is miscible with many organic solvents including chlorinated hydrocarbons and aromatic hydrocarbons. It reacts quickly with water to form HCl and SO2. Thionyl chloride is stable at room temperature however, slight decomposition occurs just... 

Physical Properties. Sulfur dioxide [7446-09-5] SO2, is a colorless gas with a characteristic pungent, choking odor. Its physical and thermodynamic properties ate Hsted in Table 8. Heat capacity, vapor pressure, heat of vaporization, density, surface tension, viscosity, thermal conductivity, heat of formation, and free energy of formation as functions of temperature ate available (213), as is a detailed discussion of the sulfur dioxide—water system (215). 

Evaporative Emission. Fumes emitted from stored fuel or fuel left in the fuel dehvery system are also regulated by U.S. EPA standards. Gasoline consists of a variety of hydrocarbons ranging from high volatility butane (C-4) to lower volatility C-8 to C-10 hydrocarbons. The high volatility HCs are necessary for cold start, and are especially necessary for temperatures below which choking is needed to start the engine. Stored fuel and fuel left in the fuel system evaporates into the atmosphere. 

Addition of 15% gasoline to methanol to produce M85 fuel is an alternative. At temperatures above —6.7° C, reHable ignition of M85 fuel occurs because the gasoline provides the vapor phase necessary for ignition under choked condition. 

Note that under choked conditions, the exit velocity is V = V = c = V/cKTVM not V/cKT(/M, . Sonic velocity must be evaluated at the exit temperature. For air, with k = 1.4, the critical pressure ratio p /vo is 0.5285 and the critical temperature ratio T /Tq = 0.8333. Thus, for air discharging from 300 K, the temperature drops by 50 K (90 R). This large temperature decrease results from the conversion of internal energy into kinetic energy and is reversible. As the discharged jet decelerates in the external stagant gas, it recovers its initial enthalpy. 

Before accepting this solution, the Reynolds number should be checked. At the pipe exit, the temperature is given by Eq. (6-120) since the flow is choked. Thus, T[Pg.651]

In order to avoid the need to measure velocity head, the loop piping must be sized to have a velocity pressure less than 5% of the static pressure. Flow conditions at the required overload capacity should be checked for critical pressure drop to ensure that valves are adequately sized. For ease of control, the loop gas cooler is usually placed downstream of the discharge throttle valve. Care should be taken to check that choke flow will not occur in the cooler tubes. Another cause of concern is cooler heat capacity and/or cooling water approach temperature. A check of these items, especially with regard to expected ambient condi-... 

This chapter discusses the procedures used to calculate the temperature at which hydrates will form for a given pressure (or the pressure at which hydrates will form for a given temperature), the amount of dehydration required to assure that water vapor does not condense from a natural gas stream, and the amount of chemical inhibitor that must be added to lower the hydrate formation temperature. It also discusses the temperature drop that occurs as gas is expanded across a choke. This latter calculation is vital to the calculation of whether hydrates will form in a given stream. 

Choking, or expansion of gas from a high pressure to a lower pressure, is generally required for control of gas flow rates. Choking is achieved by the use of a choke or a control valve. The pressure drop causes a decrease in the gas temperature, thus hydrates can form at the choke or control valve. The best way to calculate the temperature drop is to use a simulation computer program. The program will perform a flash calculation, internally balancing enthalpy. It will calculate the temperature downstream of the choke, which assures that the enthalpy of the mixture of gas and liquid upstream of the choke equals the enthalpy of the new mixture of more gas and less liquid downstream of the choke. 

Another technique that can be used to account for the presence of liquids is to assume that the water and oil in the stream pass through the choke with no phase change or loss of temperature. The gas is assumed to cool to a temperature given in Figure 4-8. The heat capacity of the liquids is then used to heat the gas to determine a new equilibrium temperature. 

Indirect fired heaters (sometimes called line heaters) heat the gas stream before and/or after the choke so that the gas is maintained above the hydrate temperature. Indirect fired heaters can also be used to heat crude oil for treating, heat a hot fluid circulating medium (heat medium) that is used to provide process heat, etc. 

Figure 5-1 shows a typical LTX process. The inlet gas stream is choked at the well to 2,000 to 3,000 psi or until the temperature declines to approximately 120°F, which is well above the hydrate formation temperature. The inlet stream next enters a coil in the bottom of the low temperature separator. The stream is then cooled to just above the hydrate formation temperature with the outlet gas coming off the low temperature separator. This assures the lowest possible temperature for the inlet stream when it enters the vessel after the choke. This choke is mounted in the vessel itself. When the pressure drop is taken, the temperature will... 

As shown in Figure 5-2, the wellstreain enters the first coil at its flowing-tubing temperature and pressure. Alternatively, it could be choked at the wellhead to a lower pressure, as long as its temperature remains above hydrate temperature. 

It is perfoclly acceptable for a line heater to have an L[ equal to 0. In this case all the heat is added downstream of the choke. It is also possible to have equal to 0 and do all the heating before the choke. Most fre quently it is found that it is better to do some of the heating before the choke, take the pressure drop, and do the rest of the heating at the low er temperature that exists downstream of the choke. 

To calculate the heat duty it must be remembered that the pressure drop through the choke is instantaneous. That is, no heat is absorbed or lost, but there is a temperature change. This is an adiabatic expansion of the gas w ith no change in enthalpy. Flow through the coils is a constant pressure process, except for the small amount of pressure drop due to friction. Thus, the change in enthalpy of the gas is equal to the heat absorbed. 

Tlic heat duty is best calculated with a process simulation program hi will account for phase changes as the fluid passes throiigli ilic ctioke. It will balance the enthalpies and accurately predict the change m tcnipcrature across the choke. Heat duty should be checked for vanoits combinations of inlet temperature, pressure, flow rate, and outlet temper ature and pressure, so as to determine the most critical combination. 

In order to choose the coil length and diameter, a temperature must first be chosen upstream of the choke the higher Tj, the longer the coil L and the shorter the coil L2. In Chapter 2 we showed that the greater the LMTD between the gas and the bath temperature, the greater the heat transfer per unit area, that is, the greater the LMTD, the smaller the coil surface area needed for the same heat transfer. The bath temperature is constant, and the gas will be coldest downstream of the choke. Therefore, the shortest total coil length (L[ -I- L2) will occur when L is as small as possible (that is, Tj is as low as possible). 

Although the total coil length is always smaller when there is no upstream coil (Lj = 0), the temperature could be so low at the outlet of the choke under these conditions that hydrates will form quickly and will partially plug the choke. In addition, the steel temperature in the choke body may become so cold that special steels are required. Therefore, some guidelines are necessary to choose Tj for an economical design. 

The results were not serious. The pumps supplied water to cool the hot gases leaving an incinerator when the water flow stopped, a high-temperature trip shut down the burner. The incinerator was nev/, was still undergoing tests, and the job had not been done before. The water was recycled, and ash in it probably caused the choke [40]. 

Clearing the choke should not have been attempted until the temperature of the water was below 60°C, the foreman should have worn protective clothing, and if possible a second valve should have been fitted to the end of the drain line as described in (a) above. The accumulation of scale suggests that the water treatment was not adequate [3]. 

Gas flow through 2 in. choke-tube 20 ft long Pressure = 150 psig Temperature = 133°F... 

If the pressure ratio is less than or equal to that specified by Equation 2-67, the flow will he sonic at the choke throat and the temperature at the throat can be found from... 

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