Patent Application
20130199576
The subject matter disclosed herein relates to clearing liquid fuel supply lines in a turbomachine.
Heavy-duty turbomachines can run on natural gas but are required to have dual fuel capacity such that an alternate fuel source, such as liquid fuel, can also be used to mitigate down time of the turbomachine. Because some turbomachines predominantly run on natural gas, the liquid fuel lines, which are typically used less often, can become clogged. Residual liquid fuel can become trapped in the line and, because of the high temperatures within the turbomachine enclosure when the turbomachine is operating on natural gas or shutdown, the trapped liquid fuel can form coke that clogs orifices such as the fuel nozzles and causes valves to stick in an open, closed, or intermediate position. As a consequence, liquid fuel may not be delivered sufficiently or timely in subsequent liquid fuel mode operation of the turbomachine.
In previous systems, attempted solutions to the problem have been inefficient and costly. For example, one part of the liquid fuel line (check valve) may be water-cooled to prevent its sticking in an open, closed, or intermediate position. However, this solution does not address other parts of the liquid fuel line, such as the flow divider. As another example, a blast of nitrogen has been used to purge/drain/blowdown the liquid fuel lines. However, this is a costly solution that necessitates a modification to existing systems. Another costly solution has been the inclusion of a return line such that liquid fuel continuously circulates through the liquid fuel line; however, this system does not clean the fuel nozzles or flow dividers when the machine is not operating on liquid fuel. The costs associated with this solution include parasitic energy loss due to the operation of the circulation pumps. A low-cost and effective system and method to clear the liquid fuel supply line would be appreciated in the dual fuel turbomachine industry.
According to an aspect of the invention, a system to clear a liquid fuel supply line in a turbomachine includes a valve configured to control a flow of cleanser into the liquid fuel supply line; and a controller configured to control the valve to allow the flow of cleanser when liquid fuel is not being supplied to a combustion can of the turbomachine through the liquid fuel supply line.
According to another aspect of the invention, a method of clearing a liquid fuel supply line in a turbomachine includes stopping a supply of liquid fuel to the turbomachine; and controlling a flow of a cleanser into the liquid fuel supply line when liquid fuel is not being supplied to a combustion can of the turbomachine.
According to yet another aspect of the invention, a computer-readable medium stores instructions which, when processed by a processor, cause the processor to execute a method of clearing a liquid fuel supply line in a dual fuel turbomachine. The method includes stopping a supply of liquid fuel to the turbomachine; and controlling a flow of a cleanser into the liquid fuel supply line when liquid fuel is not being supplied to a combustion can of the turbomachine.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
When the combustion can 160 is supplied with gas, the valve 171 is closed to prevent the liquid fuel supply line 110 from supplying liquid fuel to the combustion can 160 at the same time. During this down time for the liquid fuel supply, pockets of residual liquid fuel may pool in various areas along the liquid fuel supply line 110. Purge air 150 is let into the combustion can 160 by opening the valve 175 during gas fired operation. The purge air 150 keeps the liquid fuel nozzle in the combustion can 160 cool when the combustor is firing based on a gas supply. The cooling of the nozzle within the combustion can 160 notwithstanding, the residual liquid fuel in the liquid fuel supply line 110 is heated because of the high temperature combustion in the combustion can 160 or otherwise by the surrounding air temperature in proximity to the turbomachine. The heated residual liquid fuel forms coke (petcoke) that clogs orifices (such as the nozzle for the liquid fuel supply line 110 into the combustion can 160). The coke also sticks to the internals of the 3-way valve or check valve 174. When the check valve 174 is formed as a plunger and seat, the coke may cause the plunger to be stuck to the seat such that the check valve 174 cannot open when liquid fuel is called for again. The coke may also cause the check valve 174 to be stuck open. In this case, the next time liquid fuel is called for, the flow 145 associated with the already-open check valve 174 will allow an uncontrolled supply of liquid fuel to its corresponding combustion can 160 than via other flows 145. The resulting non-uniform timing among the flows 145 of the flow divider 140 will cause a trip (or failure to operate) at startup or a failed transfer from operation on gas fuel to liquid fuel of the turbomachine 100. Also, if the coke causes the check valve 174 to remain only partially open, then, in addition to faster supply, the effected flow 145 will ultimately provide a smaller supply of liquid fuel to its corresponding combustion can 160.
According to an embodiment of the present invention, a cleanser 130 is introduced into the liquid fuel supply line 110 followed by one or more puffs of instrument air 120 to push the cleanser 130 through the liquid fuel supply line 110. The cleanser 130 is introduced into the liquid fuel supply line 110 by opening the valve 173 when the liquid fuel is not flowing in the liquid fuel supply line 110 (when valve 171 is closed and the turbomachine is operating in gas mode or is not operating at all). In one embodiment, the cleanser 130 is water. Using water as the cleanser 130 presents a low-cost solution because demineralized water is already on site for the boiler of a combined cycle system, for example. Additionally, water is injected into the combustion can 160 along with liquid fuel for emission reduction (to suppress nitrous oxide (NOx)) in a liquid fuel system.
In an alternate embodiment, steam, rather than water, may be used as the cleanser 130. Steam may be better especially during the turbomachine's operation on gas input to ensure that the combustion process is not negatively affected. Further, when the cleanser 130 is steam, the instrument air 120 may not be needed. Additionally, steam is injected into the combustion can 160 for emission reduction (to suppress NOx). In yet another embodiment, another liquid, other than water, may be used as the cleanser 130. A suitable liquid is any liquid that does not leave its own residue in the liquid fuel supply line 110. The residual liquid fuel and coke that is flushed out of the flow divider 140, check valve 174, and remainder of the liquid fuel supply line 110 can be drained out of the system by opening the valve 176 to the waste oil drain 180.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
