Patent Application
20080085220
These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings, wherein:
One object of this invention is to remove the limitations imposed by conventional external heat tracing of sample transport tubes by locating suitably-sized heating elements or cable heaters within the sample transport tubes.
Although described herein in the context of synthesis gas transport from a process vessel in which the synthesis gas is generated to an analytical system for analyzing the synthesis gas, it will be understood by those skilled in the art that the system of this invention is suitable for use in any situation in which it is desired to prevent condensable constituents of a fluid flowing through a conduit for extended distances from condensing out of the fluid, and such applications are deemed to be within the scope of this invention.
Due to the potential for corrosion from gases flowing through the system of this invention, the sample transport conduits are preferably made from 316L or 310 stainless steel. The sample transport conduits are sized to receive a heating element employed in the system. By way of example, sample transport conduits having an outside diameter in the range of about 0.375 inches to about 0.5 inches are generally large enough to accommodate cylindrical heating elements having a diameter in the range of about 0.0625 inches to about 0.125 inches. These cylindrical heating elements are available in lengths up to about 200 inches; they can be daisy-chained for longer sample transport conduit runs; and they are easily formed into bends and coils 19 as shown in
As shown in
It will be readily apparent that replacement of an internal heating element employed in the system of this invention is neither a labor-intensive nor complicated process compared to conventional external heating systems as discussed herein above because the heater elements can be accessed at the ends of the conduit runs by opening the end of a resealable connection, e.g. a typical fitting available from SWAGELOK®, where the unheated end of the internal heater element emerges, removing the inoperable heating element, inserting a new, sheathed heating element, resealing the resealable connection, and reestablishing the electrical connections with the heating element. In contrast to conventional systems, no layers of insulation need to be replaced and, because thermal cements are not used, thermocouples that control the heater and sense the temperature of the sample gas are not disturbed. Thus, once the heating element is replaced, testing of sample gases can resume.
In accordance with one embodiment of this invention, the heating elements and/or the interior surfaces of the sample transport conduit are passivated. Passivation in accordance with one embodiment of this invention may be achieved using the Restek SILCOSTEEL process of Restek Corporation, State College, Pa. Because virtually all of the surfaces of the system of this invention exposed to process gases can be passivated, the effective transport of virtually every component of the process gas is assured. Process gases from very high temperature processes can be diluted with an appropriate inert gas and transported at 1100° F. or lower as required for analysis or disposal. The dilution gases may also be preheated with internal heating elements appropriately located within the dilution gas transport lines. Sample and dilution gas lines are typically sealed so that gas samples may be transported under pressure or at lower than atmospheric pressure as required or according to the margins of safe operation established for process pressure and temperature. Appropriate lengths of passivated conduit and inerted heating elements may be pre-assembled off-site into modular sections that can be carried to a job site for quick installation, connection, and insulation by any individual with a moderate degree of technical competence. Because these heating elements can be sectionalized, they can be made up in convenient sections ahead of time and stocked as new equipment or as replacement units.
Although intended for application to the transport of hot streams of process gas for eventual analysis, the system of this invention may also be employed in the transport of hot granulated solids or liquids so long as they can be transported through internally heated tubes or pipes by gravity, pulsating or steady pressure, or agitation. In this embodiment, the effect of adding heated dilution gas would be to cause or improve transport. However, precautions must be taken when the system is employed in oxidizing environments where excess heating can cause combustion or other undesirable chemical reactions.
We have tested the system of this invention for efficacy. In one test, internally-heated sample conduits were maintained at 800° F. and undiluted synthesis gas was transported through the sample transport conduits for three days. After the test, the conduits and heating elements were inspected and found to be devoid of any coking or deposition in spite of the fact that the synthesis gas was derived from the gasification of biomass which is known to have relatively high amounts of tars.
The heating elements employed in the system of this invention were also used to replace external heaters within spool pieces and parts of a sample extraction and dilution interface. The heating elements were sheathed with passivated capillary tubing and formed into coils that were inserted into areas of the interface that would have been difficult to heat with externally wrapped cable heating elements. With internal heating, the heating elements were never required to operate at full power to maintain internal temperatures greater than 800° F.
In another test, synthesis gas at 22 bar was extracted and sent to the sample extraction and dilution interface for depressurization and dilution. The heating elements were used to maintain the pressurized synthesis gas at about 850° F. before it was depressurized. The heating elements were never required to operate at greater than 12-15% of their rated capacity to maintain the sampling equipment and synthesis gas at 850° F.
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
