Abstract:
A visual monitoring system for covered storage tanks, comprising in combination a storage tank, an Imaging Unit and a Communication Unit. The storage tank has a peripheral wall, a fixed ceiling and a floating roof that travels up and down the peripheral wall. The Imaging Unit is positioned within the covered storage tank and includes a Camera, a Microcontroller, a Power Source and a Wireless Communication Interface. The Camera is mounted on one of the ceiling or the wall adjacent to the ceiling and is focused upon the floating roof. The Communication Unit receives wireless communication signals from the Imaging Unit providing imaging data regarding the floating roof.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/717,436 filed on Oct. 23, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to the remote visual monitoring of the space between the floating roof and the fixed roof of a covered aboveground storage tank (AST). This monitoring system can be used to view visible or invisible optical wavelengths and is used to monitor for fires, leaks, mechanical problems, and other hazardous conditions, or to determine the elevation of the floating roof within the AST. Additionally, since the appearance of the space being monitored does not often change, alarm conditions or operator notifications can be triggered when the visual field of the camera changes. The monitoring system can use wired or wireless means, or a combination thereof, for communication. 
       BACKGROUND OF THE INVENTION 
       [0003]    The processing and storage of chemical compounds, such as petrochemicals, is quite widespread. Since many of these compounds can be toxic, flammable, or potentially explosive, there are grave safety concerns for personnel and for the environment. Additionally, the capital, environmental, and human costs of a disaster at a processing facility can be staggering. 
         [0004]    In the petroleum industry, each large aboveground storage tank (AST) has a roof that floats on top of the stored liquid. This prevents having a potentially explosive vapor space between the liquid and the roof of the AST. The roof typically floats on pontoons and has a flexible seal around its perimeter to minimize the escape of liquid or vapor from the inside of the AST. However, the escape of at least small quantities of liquid or vapor is inevitable. 
         [0005]    Covered AST&#39;s have a fixed roof above the floating roof that serves both to protect the floating roof and to reduce the amount of evaporation into the atmosphere. In the petroleum storage industry, a current industry practice for monitoring covered AST&#39;s is to perform manual inspections through roof hatches. A minimal visual inspection can check that the floating roof appears to be floating properly, that there is no visible liquid on the roof, and that the seal is visibly intact. Additional manual inspections include measuring the internal atmosphere to cheek that it has a volatile gas concentration that is less than prescribed limits. 
         [0006]    Manual inspection is generally non-comprehensive and, since it occurs infrequently, such as annually or monthly, it could miss the timely detection of a potentially catastrophic condition. Remote monitoring makes it operationally feasible to inspect and monitor the AST more frequently and thoroughly, thereby facilitating the detection of potentially hazardous conditions in a timelier manner. The AST can be inspected at scheduled intervals, on demand, or when monitoring devices such as gas sensors detect an anomalous condition. 
         [0007]    Another operational hazard is the overfilling of AST&#39;s. When an AST is overfilled, the elevation of the floating roof within the tank is excessive and large quantities of liquid can escape from the AST, often with dire consequences such as catastrophic fires. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The current invention is a visual monitoring system and a related method for the visual monitoring of the space between the floating roof and the fixed roof of a covered above ground storage tank (AST). 
         [0009]    This invention is presented in the context of use in the petrochemical industry where the integrity of the floating roof, the escape of liquid or gas, and fires are of great concern but it is also suitable for deployment for other industrial applications. 
         [0010]    The invention comprises two types of units that communicate using wireless means. The Imaging Unit includes at least one digital camera and at least one wireless communication link. The Communication Unit contains at least one wireless communication link and may also contain one or more wired communication links. The Communication Unit is used to relay information from the Imaging Unit to the system operator or to a remote monitoring system by wired or wireless means. The Communication Unit or the Imaging Unit may also be directly connected to an alarm system or an audible or visual alarm by wired or wireless means. 
         [0011]    The Imaging Unit is battery powered and consequently it is important to conserve power. Since the visual field being monitored by the camera does not change often, one method of conserving power is to use a low flame acquisition rate. As an example, an image frame could be captured once every hour. The frame rate is not necessarily a fixed value and could be increased if an anomalous condition is detected. 
         [0012]    Herein, an anomalous condition is any operational condition that is of concern to the plant operator including, but not limited to, the existence of flames, excessive vibration, excessive gas concentration, or the improper position of the floating roof. 
         [0013]    When compared to the current industry practice of manual inspection, major benefits of the current invention include: inspection at more frequent intervals (e.g., multiple times per day), thereby improving the probability of the timely detection of a potentially catastrophic event and avoiding the exposure of personnel to potentially hazardous conditions. It also features low power consumption, thereby allowing long-term autonomous operation. 
         [0014]    The proposed invention can also be used to optically monitor the elevation of the floating roof within the AST, thereby helping to reduce the danger of overfilling the AST. 
         [0015]    A further potential benefit of the invention is that the ease of installation and low installed cost may serve to hasten the upgrading of safety systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1 : Functional Block Diagram of the Proposed Apparatus 
           [0017]      FIG. 2 : Functional Block Diagram of the Imaging Unit 
           [0018]      FIG. 3 : Functional Block Diagram of the Communication Unit 
           [0019]      FIG. 4 : A side elevation view, in section, of a visual monitoring system for covered storage tanks. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    With reference to the block diagram in  FIG. 1 , the invention minimally comprises a Communication Unit  1  and an Imaging Unit  2  that communicate via wireless means using Antennas  3 . The configuration of the Antennas  3  is not a facet of this invention. 
         [0021]    With reference to the block diagram in  FIG. 2 , the Imaging Unit  2  comprises an Antenna  3 ; one or more digital Cameras  4 ; a Microcontroller or Microprocessor  5 ; an electrochemical Power Source  6 ; and a Wireless Communication Interface  7 . Said Wireless Communication Interface  7  can be integrated with said Microcontroller  5 , e.g., the Freescale MC13224. 
         [0022]    With reference to the block diagram in  FIG. 3 , the Communication Unit  1  minimally comprises an Antenna  3 ; a Microcontroller or Microprocessor  5 ; a Power Source  6  such as solar panels, a connection to an external power source, or an electrochemical power source; and a Wireless Communication Interface  7 . It may include additional wireless or wired interfaces. 
         [0023]    In the current embodiment of both the Communication Unit  1  and the Imaging Unit  2 , the Microcontroller  5  and Wireless Communication Interface  7  is realized using a Freescale MC13224; the Power Source  6  is a lithium-thionyl-chloride battery pack; and the Antenna  3  is a patch antenna. 
         [0024]    There are multiple variants of the current embodiment of the Imaging Unit  2 . For an Imaging Unit that is used for monitoring visible wavelengths, the Camera  4  is a Firefly MV from Point Grey Research whereas for an Imaging Unit  2  that is used for monitoring wideband thermal infrared wavelengths, the Camera  4  is a thermoImager TIM 400 from Micro-Epsilon. Additionally, a Camera  4  can be a multispectral imaging system that captures separate images for each of a plurality of bands of spectral wavelengths. Said multispectral imaging systems can more accurately detect specific anomalous conditions such as flames. 
         [0025]    Multispectral methods for flame detection are more reliable than wideband infrared methods and are well known in the existing art, but imaging multispectral sensors have not yet been employed within AST&#39;s. Because an imaging multispectral sensor provides positional information for a detected event, rather than simply an indication of the occurrence of said event, the current invention introduces the use of multispectral imaging within an AST. 
         [0026]    The Imaging Unit  2  is designed for long-term battery-powered operation and it is therefore advantageous to minimize power consumption. Acquiring a digital image from the Camera  4  requires a significant amount of power, as does transmitting said image from the Imaging Unit  2  to the Communication Unit  1 . Hereinafter we further describe the current low-power embodiment of the Imaging Unit  2 . 
         [0027]    To reduce the amount of power consumed by image acquisition, the image is acquired only when requested by the system operator or if some other device, such as a gas sensor detects an anomalous condition and subsequently signals the Imaging Unit  2  using wired or wireless means. Additionally, the current invention can be used to acquire the image at scheduled intervals. 
         [0028]    The amount of power consumed by transmitting the image from the Imaging Unit  2  to the Communication Unit  1  can be reduced by employing various encoding methods. One class of said encoding methods compresses the data from each individual image that is acquired by the Camera  4  using commonly-available algorithms such as JPEG 2000, which is lossy, or entropy coding, which is lossless. Since said compressed image comprises fewer bits of information than an uncompressed image, the power required to transmit the image is thereby reduced. 
         [0029]    A second class of said encoding methods employs motion-video encoding, such as MPEG-4 or H-264. Although the frame rate used by this invention is quite low compared to common video-encoding applications, motion video encoding is appropriate because the visual field monitored by the Camera  4  does not often change. When compared to the said encoding of individual images, motion-video encoding greatly reduces the amount of data that needs to be transmitted from the Imaging Unit  2  to the Communication Unit  1 , thereby reducing power consumption. 
         [0030]    The visual field monitored by this invention is essentially invariant unless the AST is being filled or being emptied. Therefore, a change in the visual field can be used to indicate a potentially hazardous anomaly, such as a failed pontoon, a leaking seal, or a fire. Consequently, said change can be used to trigger an alarm or an operator notification. Methods for detecting changes in a visual field are well known in the current art and are not a facet of this invention. 
         [0031]    A further aspect of this invention is that it can be used to determine the elevation of the floating roof inside of the AST. With reference to  FIG. 4 , the Imaging Unit  2  can be attached to the Ceiling  9  or Wall  11  of the AST. The location of said Imaging Unit  2  and the location of one or more visible Markers  8 , wherein said Markers are located on the Floating Roof  10 , can be determined during installation. When filling or emptying the AST, the Floating Roof  10  rises or falls within the AST, and the angle α will thereby decrease or increase, respectively. Therefore, the distance from the Floating Roof  10  to the top of the AST can be determined by using elementary trigonometry. This aspect of the invention can be used in the prevention of the overfilling of AST&#39;s. Said visible marker is any physical feature on the AST or any additional marker or marking that can be discerned using any of the visible or invisible wavelengths monitored by any Camera  4 . By using the location of a said Marker within an image from a Camera  4 , the elevation of the roof can be manually determined by a human operator. Alternatively, the location of said Marker within said image can be automatically determined using known methods from computer vision, thereby enabling the automated computation of the elevation of the Floating Roof  10 . 
         [0032]    A plurality of Cameras  4  can be integrated into a single Imaging Unit  2  to provide redundancy, to provide additional spectral coverage, or for extending the field of view. Any Camera  4  can be mounted on a pan/tilt mechanism to extend its effective field of view. Any Camera  4  can have a zoom lens for varying its field of view. 
         [0033]    A plurality of Imaging Units  2  can be deployed to improve the coverage of the area being monitored or to monitor multiple portions of the electromagnetic spectrum, such as visual and infrared. A plurality of Communication Units  1  can be deployed to provide spatial diversity or frequency diversity for the wireless signals or to provide redundant communication links for safety-critical systems. Any Communication Unit  1  or Imaging Unit  2  can employ multiple Antennas  3  for the purpose of antenna diversity or frequency diversity. 
         [0034]    The acquisition of an image can be performed at regular time intervals or image acquisition can be triggered by anomalous conditions that are detected by one or more Sensors  12 , such as a gas sensor, inclinometer, accelerometer, or optical flame sensor. 
         [0035]    As required for any particular deployment, the communication system of the Imaging Unit  2  or the Communication Unit  1  can be configured to act as a communication relay or as part of a redundant network, such as a mesh network. These capabilities are well known in the existing art. 
         [0036]    Because the Imaging Unit  2  and the Communication Unit  1  can have a minimal number of external physical connections, including the possibility of zero external connections, they can be readily protected by an environmentally-protective enclosure, thereby making them suitable for use in harsh environments. The current embodiment of the Imaging Unit  2  is intended for deployment within petroleum AST&#39;s and meets the ATEX requirements for Intrinsic Safety, although these are not requirements of the current invention.