Line heaters

In pipelines, heat is usually supplied with a line heater. In the design of a line heater, sufficient heat must be supplied to the fluid such that it is never at a temperature where a hydrate will form. That means the fluid must be heated well above the hydrate formation temperature. As it flows through the line it will cool, losing energy to the environment. Once it arrives at its destination, usually the plant site, it must be warmer than the hydrate temperature. It may be necessary to use more than one line heater. 

From a hydrate melting standpoint it is possible in the winter time to have too cold a liquid temperature and thus plug the liquid outlet of the low temperature separator. It is easier for field personnel to understand and operate a line heater for hydrate control and a multistage flash or condensate stabilizer system to maximize liquids recovery. 

In fire tube type heaters, the coils are immersed in a bath of water. The water is heated by a fire tube that is in the bath below the coils. That is, the fire tube provides a heat flux that heats the water bath. The water bath 

Since the bath fluid is normally water, it is desirable to limit the bath temperature to 190°F to 200°F to avoid evaporating the water. If higher bath temperatures are needed, glycol can be added to the water. 

In order to adequately describe the size of a heater, the heat duty, the size of the fire tubes, the coil diameters and wall thicknesses, and the cor lengths must be specified. To determine the heat duty required, the maximum amounts of gas, water, and oil or condensate expected in the heater and the pressures and temperatures of the heater inlet and outlet must be known. Since the purpose of the heater is to prevent hydrates from forming downstream of the heater, the outlet temperature will depend on the hydrate formation temperature of the gas. The coil size of a heater depeiuLs on the volume of fluid flowing through the coil and the required heat duty. 

Special operating conditions such as start up of a shut-in well must be considered in sizing the heater. The temperature and pressure conditions found in a shut-in well may require additional heater capacity over the steady state requirements. It may be necessary to temporarily install a heater until the flowing wellhead temperature increases as the hot resei voir fluids heat up the tubing, casing, and surrounding material. 

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Note Alarms and shutdowns as shown are not to be considered as meeting any minimum safety requirement but are shown as representative of types used for controi systems. Schematic Alarm/Shutdown Hydrocarbon Low Pressure Hot oil or Glycol Amine Label Description Line Heater Reboiler Steam Heater Salt Heater Reboiler Reboiler ... 

In an indirect bath heat exchanger, the heating medium provides Iil u to an intermediary fluid, which then transfers the heat to the fluid h)cuig heated. An example of this is the common line heater used on many gas well streams to keep the temperature above the hydrate formal ion lem perature. A fire tube heats a water bath, which provides heat to tlie v.all siieam flowing through a coil immersed in the bath. Details pertaining to dcsi jit of indirect bath heaters are presented in Chapter 5. 

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. 

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. 

Volume 1, Chapter 9 explains the criteria for choosing a diameter and wall thickness of pipe. This procedure can be applied to choosing a coil diameter in an indirect fired heater. Erosional flow criteria will almost always govern in choosing the diameter. Sometimes it is necessary to check for pressure drop in the coil. Typically, pressure drop will not be important since the whole purpose of the line heater is to allow a large pressure drop that must be taken. The allowable erosional velocity is ffiven bv ... 

The previous discussion focused on the use of indirect fired heaters as line heaters to provide the necessary heat to avoid hydrate formation at wellstream chokes. Indirect fired heaters have many other potential uses in production facilities. For example, indirect fired heaters can be used to provide heat to emulsions prior to treating, as reboilers on distillation towers, and to heat liquids that are circulated to several heat users. The sizing of indirect fired heaters for these uses relies on the same principles and techniques discussed for wellstream line heaters. 

Figure 5-4. Dimensions of standard line heaters. (From Smith Industries, Inc.j...

Design a line heater for each of the 10 wells that make up the total 100 MMscfd field rate. That is. each well flows at 10 MMscfd. 

Figure 10-4E. Longitudinal finned-tube tank suction direct line heater. (Used by permission Brown Fintube Co., A Koch Engineering Co., Bui. 4-5.)...

Instrument Acquisition mode Ionization mode MS quadrupole MS source MSD transfer line heater Ion masses... 

Line heaters could be installed at the wellhead to increase the inlet gas temperature from 85°F to 125°F. Figure 8.5 shows the pipeline temperature increase caused by the combined prevention methods of burial and wellhead heating. Use of these two methods permitted the methanol concentration in the free water phase to be reduced to approximately 14 wt% to prevent hydrate formation in the line. It should, however, be noted that heating may increase the amount of corrosion in the line. 

A nitrogen pressurized fuel system provided fuel to the atomizer at well controlled temperatures up to 240°F. Preheating was provided by a combination of reservoir and line heaters. Atomizer air was obtained from the laboratory air supply. 

Separator line would constantly plug up Separator line improperly designed Reconfigured line and added line heaters... 

Ucarkool. [Union Carbide] Heat transfer fluid fw gas compression and line heater applies. 

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