Patent Publication Number: US-2013232964-A1

Title: Hybrid power system

Description:
FIELD 
     There is described a hybrid power system that was developed for providing power to hydraulic pumps on drilling rigs, but has other potential applications. 
     BACKGROUND 
     There is a need to reduce greenhouse gas emissions produced by drilling rigs. Drilling rigs generally have an electric power source that is considered to be a “green” emission free source of energy. This electric power source is capable of powering hydraulic pumps that provide hydraulic fluid to working systems in most, but not all situations. 
     SUMMARY 
     There is provided a hybrid power source which includes an electric power source, a first hydraulic pump powered by the electric power source, a hydrocarbon burning power source, and a second hydraulic pump powered by the hydrocarbon burning power source. A hydraulic fluid output is fed by a combined output from the first hydraulic pump and the second hydraulic pump. A controller is provided for dynamically calculating hydraulic fluid requirements at the hydraulic fluid output as work is performed. The hydraulic fluid requirements are primarily provided by the first hydraulic pump powered by the electric power source and supplemented, as directed by the controller, by the second hydraulic pump powered by the hydrocarbon burning power source. 
     The hybrid power system, as described above, is capable of reducing greenhouse gas emissions, while also providing redundancy against a possible failure of the electric power source. It also extends the useful life of the hydrocarbon burning power source, which will not be needed and can be shut down for a large proportion of the time. The sensor input into the controller will vary with each application. For a lifting application, a weight of a load to be lifted and distance the load has travelled over time will be used. The controller must also know the horse power requirements for the first hydraulic pump and the second hydraulic pump, along with output flow rates from each pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein: 
         FIG. 1  is a schematic of a hybrid power system. 
     
    
    
     DETAILED DESCRIPTION 
     A hybrid power system generally identified by reference numeral  10 , will now be described with reference to  FIG. 1 . 
     Structure and Relationship of Parts: 
     Referring to  FIG. 1 , hybrid power system  10  uses primarily a first pair of hydraulic pumps  12   a  and  12   b  powered by a pair of 100 horsepower electric motors  14   a  and  14   b . Electricity to power electric motors  14   a  and  14   b  is provided by an electric power supply  15 . A second pair of hydraulic pumps  16   a  and  16   b  powered by a hydrocarbon burning power source  18 , typically a 500 horsepower diesel engine, supplements power provided by first pair of hydraulic pumps  12   a  and  12   b  based upon hydraulic fluid requirements at hydraulic fluid output  20 . Hydraulic fluid output  20  is fed by a combined output from both first pair of hydraulic pumps  12   a  and  12   b  and second pair of hydraulic pumps  16   a  and  16   b . The extent to which second pair of hydraulic pumps  16   a  and  16   b  are utilized to supplement first pair of hydraulic pumps  12   a  and  12   b  is controlled by a programmable logic controller  22  for dynamically calculating hydraulic fluid requirements at hydraulic fluid output  20  as work is performed. Hydraulic fluid output  20  supplies hydraulic fluid to a hydraulic lift system  24 . Sensor data, such as weight of a load being lifted and distance travelled by the load over a time interval, is provided to controller  22  from sensors  26  to regulate use of second pair of hydraulic pumps  16   a  and  16   b.    
     Operation: 
     Referring to  FIG. 1 , hybrid power system  10  begins performing work using first pair of hydraulic pumps  12   a  and  12   b  which are powered by electric motors  14   a  and  14   b , respectively. Hydraulic fluid output  20  supplies hydraulic fluid to hydraulic lift system  24 . Sensor data from sensors  26  attached to hydraulic lift system  24  is provided to controller  22  to regulate use of second pair of hydraulic pumps  16   a  and  16   b . When required, second pair of hydraulic pumps  16   a  and  16   b , which is powered by a hydrocarbon burning power source  18 , supplements the power provided by first pair of hydraulic pumps  12   a  and  12   b . This causes an increase in the amount of hydraulic fluid at hydraulic fluid output  20  and increases the work capabilities of hydraulic lift system  24 . 
     EXAMPLE 1 
     Off Bottom Lift 
     This example deals with a lift of a drill string off bottom in an off shore drilling rig. If the weight of the drill string is 70,000 pounds and the target speed is to raise the drill string at a rate of 10-15 meters per minute calculations can be made as to a combined flow rate required from the first pair of hydraulic pumps  12   a  and  12   b  powered by the electric motors  14   a  and  14   b  and the second pair of hydraulic pumps  16   a  and  16   b  powered by the hydrocarbon burning power source  18 . That combined flow rate can be converted into a combined horse power requirement to produce the combined flow rate. Assuming that a total horse power of 250 horse power is required to get the 70,000 pound drill string moving at the target rate of 10-15 meters per minute. The electric power source has a finite horse power limit. In that instance, the controller may determine that 115 horse power can be provided by the electric power source and that the remaining 135 horse power will have to be supplemented with the hydrocarbon burning power source. The contributions of the first pair of hydraulic pumps  12   a  and  12   b  and the second pair of hydraulic pumps  16   a  and  16   b  to the combined flow rate of hydraulic fluid will be governed according to the power contributions of the electric power source and the hydrocarbon burning power source. 
     EXAMPLE 2  
     Drill String in Motion 
     This example deals with a drill string in motion which is approaching surface. A drill string at rest has some initial inertia to overcome, as well as a column of water pressing down from above. When the drill string is in motion, it takes less power to keep it in motion and the weight decreases in a linear fashion at the drill string reaches surface at a rate of 6.6 pounds per foot raised. If the weight of the drill string has decreased to 20,000 pounds, 96 horse power is required to maintain the drill string in motion. As 96 horse power is within the capacity of the electric power source, the controller shuts down the hydrocarbon fuelled power source and has all hydraulic requirements provided by the first pair of hydraulic pumps  12   a  and  12   b  powered by the electric power source. 
     Calculations: 
     In order to perform the calculations in Example 1 and Example 2, some sensor data is required. The depth of the drill string must be determined through the use of a depth encoder and its total weight at a given depth calculated. The speed that the drill string is travelling over a given time interval must also be determined The horse power requirements and the flow output of the first hydraulic pump must be known. The horse power requirements and the flow output of the second hydraulic pump must be known. 
     In this patent document, the word “comprising” is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article “a” does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. 
     The following claims are to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, and what can be obviously substituted. Those skilled in the art will appreciate that various adaptations and modifications of the described embodiments can be configured without departing from the scope of the claims. The illustrated embodiments have been set forth only as examples and should not be taken as limiting the invention. It is to be understood that, within the scope of the following claims, the invention may be practiced other than as specifically illustrated and described.