subject: something you should know about nitrogen generator [print this page] something you should know about nitrogen generator
[0002] 1. Field of the Invention
[0003] The present invention is directed to nitrogen generators, and in particular, portable cryogenic nitrogen generators.
[0004] 2. Description of the Related Art
[0005] Inert gases are widely used in many industrial processes. For example, nitrogen gas is commonly used in conjunction with operation of a drilling rig for oil, gas, or geothermal wells, as well as for post drilling operations. In particular, nitrogen is injected into the down-hole region during a drilling operation, to remove drill cuttings.
[0006] In the art of well drilling, tubular casings are typically inserted into the wells so as to secure the perimeter of the wellbore. In some wells, multiple casings are secured at the surface of the well to lower down-hole locations. Other types of casings, called liners, are sometimes used to extend from the lower-most casing into the lower-most portion of the wellbore. Drilling fluids, such as drilling mud, are often used when large flows of water are present in the well. The drilling mud is circulated down the drill string, through the drill bit, and up the annular region between the drill string and the wellbore or casing. Gas, such as Nitrogen gas, may be injected into the down-hole region to provide faster drilling when substantial amounts of water are not present in the well.
[0007] In the past, air has been used as the principal down-hole drilling fluid for lower water content drilling. The air can be combined with a surfactant, foaming agent, water, and/or mud for different applications. The primary advantages of straight air drilling are greatly increased penetration rates, greater bit footage, and fewer down-hole drilling problems.
[0008] However, drilling with air does raise a number of disadvantages. For example, injection of high-pressure air into a down-hole during a drilling operation increases corrosion rates and raises the risk of explosions or fire due to the presence of high levels of oxygen in the pressurized air. In order to reduce the risk of explosions or fire, it has been known to reduce the temperature of the injected air, or to replace the air with an inert gas, such as Nitrogen.
[0009] One option for supplying nitrogen gas to the down-hole region of a well during a drilling operation is to ship containerized nitrogen to the drilling site and pump the nitrogen gas into the well at a pressure from about 200 psig to 10,000 psig. However, the shipment of containerized nitrogen to a drilling site, which may be in a remote location, can be expensive. Thus, it is more desirable to generate nitrogen gas at the site of the drilling operation.
[0010] One option for producing nitrogen gas at a drilling site is disclosed in U.S. Pat. No. 6,041,873 issued to Michael, the entire contents of which is hereby expressly incorporated by reference. The Michael patent discloses a portable unit that produces nitrogen gas through non-cryogenic systems including membrane separation units.
SUMMARY OF THE INVENTION
[0011] One drawback of non-cryogenic devices is that efficiency drops off rapidly as purity increases. For example, it has been found that portable membrane separation units can provide 95% pure nitrogen gas at a flow rate sufficient for drilling operations. However, these units are not practical for generating an appropriate nitrogen flow at purities of above 95%, and in particular, purities above 99.0%.
[0012] One aspect of the present invention includes the realization that cryogenic nitrogen generators can be made sufficiently portable to provide practicable sources of higher purity nitrogen gas for drilling operations.
[0013] Another aspect of the present invention includes the realization that standard sized containers can be used to provide a protective housing during transportation and operation of the cryogenic nitrogen generator. By using standard size containers to form a housing for a cryogenic nitrogen generator, such as a cryogenic distillation and associated heat exchanger unit, the device can be shipped to a drilling site and efficiently and quickly assembled into an operative state. For example, a cryogenic nitrogen generator can include an air preparation unit and a cryogenic distillation and associated heat exchanger unit. The air preparation unit typically will include an absorption device, such as a Pressure Swing Absorption (PSA) or a Temperature Swing Absorption (TSA) unit. Optionally, the air preparation unit can also include one or a plurality of air compressor units. The air preparation unit can be configured to fit within a standard ISO container resting horizontally. However, a cryogenic distillation unit is quite tall. For example, typical cryogenic distillation units, also known as "cold boxes," can be as tall as 30 feet or more to produce Nitrogen gas of better than 99% purity. Thus, the distillation unit can be separately housed in a standard ISO container. With these units separately housed as such, they can be transported to and through virtually any country in the world using standard sized trucks or via ocean-going ships. Additionally, once delivered to a drilling site, the separate components can be connected and operated while they remain in the separate containers.
[0014] A further advantage in using ISO containers is that such containers include standard anchoring points which can be connected together. For example, anchoring points of each container can be connected together so as to provide further stability for plumbing connections between the containers and also to provide further stability to the container housing the distillation unit. For example, because the distillation unit is tall, connection to another container, and in particular another ISO container, provides further stability to the total system.
[0015] Typical cryogenic air separation plants are designed to remove normal levels of carbon dioxide, nitrogen generator,hydrocarbons, sulfur containing compounds, and other acid gases in ambient feed air. However, ambient air contaminate levels at oil or gas exploration drilling and recovery sites can be higher than normal levels, making it necessary to use additional precautions to ensure safe air separation plant operation. Accordingly, in one embodiment, the air preparation unit also includes a catalytic converter to remove hydrocarbons from an ambient air stream, preferably before the air stream enters the absorption device.
