APPARATUS AND METHOD FOR VENTING AND DEPRESSURIZATION OF AN ODORANT INJECTION SYSTEM

Abstract

The apparatus and method for venting and depressurization of an odorant injection system may be used on special LNG tankers that have onboard gasification equipment, on land or elsewhere. Odorant injection systems may operate at high pressures on an intermittent basis. On some occasions, the odorant is drained from a pressurized system and disposed of in inappropriate ways. The present invention depressurizes an odorant injection system and transfers the unwanted liquid odorant back into an odorant tank where it can be reused when the odorant injection system is restarted.

Description

DESCRIPTION OF THE PRIOR ART

Natural gas is a clear, odorless and tasteless gas as it comes from the ground. For safety purposes, odorant is commonly injected into the natural gas before it is distributed to customers. There are many prior art odorant injection systems including U.S. Pat. No. 6,142,162 owned by the assignee of the present application, which is incorporated herein by reference. Other odorant injection systems are disclosed in U.S. Pat. Nos. 5,406,970 and 6,208913 which are owned by Y-Z Industries, Inc.

On land, natural gas is commonly transported in pipelines. In order to transport natural gas in a ship, it is first liquefied and stored in large land based tanks before it is loaded onto the ship. One cubic foot of liquefied natural gas (LNG) represents about 600 cubic feet of natural gas. Liquefaction saves space and makes LNG economical to ship on the high seas.

Natural gas is typically liquefied in geographic areas of the world where natural gas is produced, but where there is little commercial market for the gas, such as Indonesia, Trinidad and the Middle East. LNG is commonly shipped on LNG tankers to markets where it is used, such as Japan, the United States and Europe. LNG it typically offloaded from these tankers to large tank based storage facilities on land where the LNG is gasified. Depending on local needs, the LNG may be gasified on a continuous or intermittent basis.

Special LNG tankers have been developed which regasify the LNG onboard instead of offloading the LNG to a large land based storage tank. These special LNG tankers often moor offshore to a buoy and gasify the LNG which is injected into a pipeline for transport to the pipeline distribution grid onshore. This offshore gasification process may be continuous or it may be intermittent; it make take several days to gasify the LNG and empties the tanker.

Odorant injection systems are used on some of these special LNG tankers with onboard gasification facilities. The onboard odorant injection systems need to depressurize between the intermittent periods of gasification to reduce the chance of leaks and stress on the system. Leaks in odorant injection systems tend to have an in terrorium effect among crew and officers because they sense a gas leak. There is a need for improved systems to depressurize and vent odorant injection systems when not in use, such as between the intermittent periods of gasification on special LNG vessels and elsewhere.

SUMMARY OF THE INVENTION

In the past, unwanted odorant has not always been treated with respect. For example, there are rumors that unwanted odorant has been collected in a tin can or glass jug when an odorant injection system has been depressurized. Other rumors indicate that unwanted odorant has sometimes been thrown on the ground or disposed of in other inappropriate ways.

The present invention is a system that returns unwanted odorant from a depressurized odorant injection system to an odorant tank(s) which is sometimes called an odorant tote in the industry. The odorant can thus be reused when the odorant injection system is restarted. The present invention also filters vapors from the odorant tank(s) before they are vented to atmosphere. If widely implemented, this system will reduce improper disposal of odorant when an odorant injection system is depressurized and it will reduce airborne discharge of stinky gas that has a high concentration of odorant. The present invention may be used onboard a LNG vessel and elsewhere.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an odorant injection system with flow arrows indicating the odorant flow from the odorant tanks to and odorant injection line.

FIG. 2 is a schematic of an odorant injection system with flow arrows indicating the depressurization of the system and venting of filtered vapors to atmosphere.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic of an odorant injection system 10 with flow arrows indicating the odorant flow from the odorant tanks 12 and 14 to the odorant injection conduit 16. This odorant injection system may be located on a specialized LNG tanker, as previously described, or it may be located elsewhere. For purposes of this illustration, the odorant injection system 10 will be located on the specialized LNG tanker and will be used to odorize the gasified LNG before it leaves the tanker. The regasification activity is intermittent.

A downcomer 18 is located in the first odorant tank and is in fluid communication with a valve 19, a conduit 20, a valve 22, a conduit 24, a valve 26, a conduit 28, a valve 30 and the first odorant filter 32. During the injection process, as illustrated by the flow arrows in FIG. 1, liquid odorant 8 flows from the first odorant tank 14, through the downcomer 18, the valve 19, the conduit 20, the valve 22, the conduit 24, the valve 26, the conduit 28, the valve 30 to the first odorant filter 32.

A second downcomer 34 is located in the second odorant tank and is in fluid communication with a valve 36, a conduit 38, a valve 40, a conduit 42, the valve 26, a conduit 46, a valve 48 and the second odorant filter 50. During the injection process, as illustrated by the flow arrows in FIG. 1, liquid odorant flows from the second odorant tank 14, through the second downcomer 34, the valve 30, the conduit 38, the valve 40, the conduit 42, the valve 26, the conduit 46, the valve 48 to the second odorant filter 50.

It is typical for an odorant injection system to have dual filtration of the odorant as it flows from the odorant tank to the odorant pumps. The first filter 32 is in fluid communication with valve 60, conduit 62, and the common odorant feed conduit 64. The second filter 50 is in fluid communication with the valve 72, the conduit 73 and the common odorant feed conduit 64. During the injection process, as illustrated by the flow arrows in FIG. 1, liquid odorant flows through the first odorant filter 32 and the second odorant filter 50 through the common odorant feed conduit 64, to the first odorant pump 70 and the second odorant pump 80.

As is well know to those skilled in the art, blanket pressure in the range of from about 20 psi to about 25 psi is kept on the first and second odorant tanks to help keep the conduits from the odorant tanks to the odorant pumps at least partially filled with liquid odorant. Tank blanket pressure from the system cabinet, not shown, enters the system through conduit 90 as indicated by the flow arrow. Blanket gas flows through valve 92, tee, 96, valve 98, conduit 100, valve 102 and into the top of the first odorant tank 12. Blanket gas flows through the valve 92, the tee, 96, the valve 104, the conduit 106 and the valve 108 to the top of the second odorant tank 14. Because blanket gas is relatively low in pressure, leaks in the odorant injection system seldom develop between the odorant tanks and the injection pumps. However, downstream of the odorant pumps, the odorant may reach pressures in the range of about 1400 psi. These relatively higher pressures, especially those in the odorant injection conduit 16 may cause leaks; it is therefore desirable to depressurize the odorant injection conduit 16 when not in use.

Odorant 8 is pressurized in the first pump 70 and exits the first pump at the outlet 120 and passes through conduit 122, a valve 124, a conduit 126, a tee 128, a valve 78 and enters a flowmeter 132. Likewise, odorant 8 is pressurized in the second pump 80 exits the second pump 80 at the outlet 134, and passes through a conduit 136, a valve 138, the tee 158, the valve 130 and enters the flowmeter 132.

Odorant 8 exits the flowmeter 132 through a flowmeter outlet 142 and passes through a valve 144, a conduit 146, a check valve 148, a conduit 150, a valve 152 and enters the odorant injection conduit 16.

FIG. 2 is a schematic of an odorant injection system with flow arrows indicating the depressurization of the system and venting of filtered vapors to atmosphere. The structure depicted in FIG. 1 and FIG. 2 is the same, but the flow of odorant through FIG. 1 is the opposite of the flow through FIG. 2 as indicated by the flow arrows in each respective figure. In FIG. 1, the odorant injection system 10 is pumping liquid odorant into the odorant injection conduit 16. In FIG. 2, the odorant depressurization system 160 is depressurizing the odorant injection conduit 16 and venting filtered vapors to atmosphere. The odorant depressurization system 160 is composed generally of the bypass conduit 162, the vapor filter 164, and valves which will be described in detail below.

During depressurization odorant flows from the odorant injection conduit 16 through the valve 152, a conduit 167, a valve 166, the bypass conduit 162, a valve 168, and into a tee 169 where the flow splits and passes through the valve 22, the conduit 20, the valve 19, the downcomer 18 and back into odorant tank 1. Odorant from the tee 169 also passes through the valve 40, the conduit 38, the valve 30 and the downcomer 34 into the second odorant tank 14.

Vapors 6 from the first odorant tank 12 pass through the valve 102, the conduit 100, the valve 98, a tee 178, a valve 170, a conduit 172 and into the vapor filter 164, as indicated by the flow arrows. Vapors 6 from the second odorant tank 14 pass through the valve 108, the conduit 106, a valve 104, the tee 178 and merge with the stream from the first odorant tank. The combined flow of vapors passes through the valve 170, the conduit 172 and into the vapor filter 164. Filter media, not shown, fills the inside of the vapor filter. Activated charcoal is a suitable filter media. Other types of filter media may be used or several types of media may be used in the vapor filter. After passing through the filter media, the filtered vapors 175 exit the vapor filter 164 at the exit port 174 as indicated by the flow arrow. The filtered vapors 175 have a lower concentration of odorant than those exiting the odorant tanks, 12 and 14.

Operational Description of FIGS. 1 and 2

Referring to FIG. 1, the purpose of the odorant injection system 10 is to inject odorant 8 from the tanks 12 and 14, under pressure into the odorant injection conduit 16. In FIG. 1, the following valves are in the open position during injection of odorant: 19, 22, 26, 30, 32, 48, 60, 68, 72, 92, 98, 102, 104, 108, 124, 130, 144, 152. In FIG. 1, the following valves are in the closed position during injection of odorant: 166, 168, 170 and 176. Odorant flows from the odorant tanks, the odorant filters, the odorant pumps, the odorant flowmeter to the odorant injection line as indicated by the by the flow arrows in FIG. 1.

Referring to FIG. 2, the purpose of the depressurization system 160 is to depressurize the odorant injection line 16, transfer unwanted odorant back into the odorant tanks 12 and 14 and vent purified vapors to atmosphere. In FIG. 2, the following valves are in the open position during the depressurization of the odorant injection system: 19, 22, 98, 102, 104, 108, 152, 166, 168, and 170. In FIG. 2 the following valves are in the closed position: 26, 130, 144 and 176 as indicated by the by the flow arrows in FIG. 1. The odorant flows from the odorant injection line, through the bypass line to the odorant tanks, as indicated by the by the flow arrows in FIG. 1. Vapors leave the odorant tanks, pass through the filter and are vented to atmosphere as indicated by the flow arrows in FIG. 1.

As an example, the present invention is capable of depressurizing a ¾ inch odorant injection line that is approximately 600 feet long from the odorant injection system cabinet, not shown, to the point of injection into the gas being offloaded from the LNG ship. A typical odorant tote may hold 250 gallons of odorant so the tote may weigh more than 1700 lbs. Heavy items like the odorant tote need to be lifted from sea level to the deck of the LNG tanker by an on-board crane. Two totes are often used in the odorant injection system. The deck of the LNG tanker is about 3 stories from sea level. The odorant injection system cabinet needs to be near the totes, which need to be near the crane. This location necessitates a long odorant injection line that is several hundred feet in length. The present invention can reduce the pressure in the odorant injection line from about 1400 psi to about zero psig. After depressurization, it takes some odorant systems about 15 to about 20 minutes to build up the necessary pressure in the aforementioned odorant injection line, before offloading can begin. Odorant is not put in LNG because it can crystallize.

Odorant injection systems are often controlled by a programmable logic controller (PLC), personal computer (PC), flow computer or other automated means that is often housed in the odorant injection cabinet, as is well know to those skilled in the art. The PLC, PC, flow computer or other automated means controls the operation of the odorant injection pumps, valves and other necessary components to control the injection system. The PLC, PC, flow computer or other automated means may also be used to control the valves in the present invention. In the alternative, the present invention may be manually operated.

Claims

1. An odorant depressurization system for depressurizing at least a portion of an odorant injection system in an environmentally friendly manner, the odorant injection system having at least one odorant injection pump, at least one odorant container and at least one odorant injection conduit in fluid communication with the at least one odorant injection pump and at least one natural gas conduit, the odorant depressurization system comprising: at least one bypass conduit in fluid communication with the odorant injection conduit and the at least one odorant container;at least one vapor filter in fluid communication with the at least one odorant container and atmosphere;a plurality of valves to open the bypass conduit to fluid communication from the odorant injection conduit to the at least one odorant container and to close the bypass injection conduit to fluid communication with other portions of the odorant injection system; anda plurality of valves to open the at least at least one vapor filter to fluid communication from the at least one odorant container and to open the at least one vapor filter to atmosphere to vent purified vapor from the at least one odorant container.

2. A system for venting vapors from an odorant injection system to atmosphere, said vapors having a reduced concentration of odorant, the venting system comprising: means for transporting odorant from an odorant injection conduit into an odorant container, the transporting means including valving to selectively direct the flow of odorant from the injection conduit into the odorant container; andmeans for filtering vapor from the odorant tank to reduce the concentration of odorant in said vapor before it is vented to atmosphere, the filter means including valving to selectively direct the flow of vapors from the odorant container, through the filter means and thereafter into the atmosphere.

3. A method for venting vapors and depressurization of an odorant injection line comprising the following steps: depressurizing the odorant injection line and allowing the odorant in the odorant injection line to flow back into an odorant container; andventing the odorant container and filtering the vapors that are vented to reduce the concentration of odorant in the vapors before said vapors are vented to atmosphere.

4. In combination, an odorant injection system with integrated depressurization system for use on an LNG tanker with onboard gasification systems, the odorant injection system with integrated depressurization system including: an odorant injection system having; at least one odorant storage tank to contain a supply of liquid odorant;at least one odorant injection conduit;at least one odorant injection pump to pump liquid odorant from the at least one odorant storage tank to the at least one odorant injection conduit; andconduits providing a fluid flow path between the at least one odorant storage tank, the at least one odorant injection pump and the at least one odorant injection conduit;an odorant depressurization and venting system having;a bypass line to drain liquid odorant from the at least one odorant injection conduit into the at least one odorant storage tank;a vapor filter to purify vapors from the at least one odorant storage tank, before the vapors are vented to atmosphere;means for controlling the odorant injection system and odorant depressurization system including valves to direct the liquid odorant flow path into the at least one odorant injection conduit when the system is injecting odorant and to direct the liquid odorant from the at least one odorant injection conduit to the at least one odorant storage tank when the system is being depressurized.