Green Well Renewable Power

History
The motion “kinetic energy” of flowing water and wind were harnessed by water wheels, crude early wind turbines, was used to power pistons within cylinders, etc., which eventually led to the development of the “heat engine”. Steam engines are among the oldest form of heat engines, dating back to the 18th century. Heat was used to boil water to produce steam to generate kinetic energy to power the piston of the steam engine in order to perform mechanical work, using steam as its working fluid.

The original steam engine was a single piston reciprocating back-and-forth that was actuated by a mechanical slide valve. A “crank” was connected to an output shaft of the piston in order to turn reciprocating motion into rotary motion power. The weaknesses of the steam engine technology were: (1) Poor vector angles (the ninety degree vector angle is optimum) were produced by the crank during its rotation, which dramatically reduced the mechanical efficiency of conversion of the piston power output from an efficiency of near ninety-five percent (95%) to approximately thirty-five (35%);


and, (2) the problematic mechanical nature of the slide valve actuation method that also restricted the flow of steam into the cylinders; and, (3) the extremely low thermodynamic efficiency of the Rankine cycle, which requires much more heat input due to the phase change (latent heats) needed to boil the water into steam than is required by thermodynamic cycles later invented that remain in the gaseous phase, such as the Otto cycle (gasoline engine), Diesel cycle, Sterling (produces power by alternately heating and cooling a working fluid) and Brayton cycle (the jet engine and gas-fired turbine engine).

It was later determined that the Carnot Thermal Efficiency of the cycle - solely determined by the temperature difference between the highest temperature used in the cycle as the heat source and the lowest temperature used in the cycle for heat rejection (the Delta temperature of the cycle) - limits the amount of power that may be generated by any power cycle. For this reason, it is much more challenging to produce power from heat sources having lower temperature heat than from higher temperature heat sources. Fossil fuel powered combustion engines generally produce high temperatures (greater than three thousand degrees Fahrenheit) while state-of-the-art geothermal systems are able to operate at a much lower thermodynamic efficiency on the order of thirteen percent (13%) from heat sources with temperatures of only a few hundred degrees Fahrenheit.

Modern combustion engines use the low-efficiency crank-style power transfer system via a crankshaft connected to multiple pistons, which limits the mechanical efficiency of these engines to only the twenty-five percent (25%) range, even though they combust fuel at very high temperatures. This range of power efficiency is even lower than the early steam driven free-piston engine because the pistons must compress air for combustion on their upstroke and overcome greatly increased friction loss.

Jet aircraft engines and gas fired turbine engines attain much higher mechanical efficiencies, on the order of eighty-five percent (85%) and have a much more favorable power-to-weight ratio, being the engine's power output in relationship to its weight; and, therefore, turbine engines have become the standard in the power industry. However, the thermodynamic efficiency of turbine engines is limited to only about thirty percent (30%) because upwards to two thirds of the power of the output turbine is used to compress air into the combustor in order to perform combustion. Turbine engines also suffer from severe limitations such as (1) very high initial and maintenance costs, (2) long-lead delivery times, (3) poor operational flexibility as they will not withstand pressure changes, (4) will not operate on dual-phase working fluids, (5) are generally designed to operate at reasonably low pressures relative to oil and gas well operating pressures and have very low efficiency at very low pressures (generally associated with low temperature heat sources), (6) size and weight restrictions, (7) noise and vibration restrictions, (8) complex control system requirements, and (9) complex bearing lubrication system requirements.

Combustion powered “free-piston” engines with no mechanical connection between the piston and a crankshaft were invented in the 1920s (hence the name free-piston). The design allows for improved combustion and less friction and their supporters believe the engines could be far more efficient in generating electricity than either conventional generators or newer fuel-cell technology. Therefore, extensive research is now focused on the great potential of free piston engines with their many advantages.

Sandia National Laboratory’s diesel powered free-piston engine, with two opposing free-pistons directly powering a linear alternator located between the two pistons claims a high mechanical efficiency in the order of ninety percent (90%). It also claims the highest thermodynamic efficiency of any engine ever designed, in the order of fifty-seven percent (57%). The high thermodynamic efficiency is largely due to the use of the Diesel cycle that remains in the gaseous phase and the high Carnot thermal efficiency of the high temperature diesel combustion. The high mechanical efficiency is attributed to the fact that the power output from the piston is not converted to rotary motion and power is transmitted at the optimum ninety degree vector angle, doing away with all of the mechanical gearing and thus eliminating poor vector angles associated with the inefficient crankshaft method of power transfer.

Perhaps the biggest issue regarding free-piston engine faced by researchers of this promising technology is control. In a conventional engine, the movement of the pistons is constrained by the rods and crankshaft that makes it necessary to use some sort of active control mechanism that they have not yet successfully developed.

Linear Power Ltd’s Proprietary Free-Piston Engine Technology
The goal of Linear Power, Ltd’s proprietary technology is to produce a free-piston engine that is not powered by internal combustion, but may be powered by any kinetic energy resource or heat resource that may be used to produce kinetic energy. Research and development efforts led to the filing of two patented alternate means of active control actuation and stroke length control of the back-and-forth motion of the power piston: (1) high-speed cooled solenoid actuation; and, (2) pressure actuation.

Extensive engineering and prototype development resulted in the determination that the pressure actuated method because of its low cost, simplicity, robustness, automatic timing, and very high speed of operation is substantially superior to the cooled solenoid valve actuation method. Conventional solenoid valves overheat with cycles speeds in excess of three hundred cycles per minute, which led to the patent regarding cooling the solenoid valve to achieve higher speed operation to solve the problem. However, solenoid valves are very expensive in large sizes for high flow rates as the gas must physically pass through the valve, must have a supply of electricity, consume substantial amounts of electrical power, and must have a complex system of proximity sensors and computer controllers in order to effectively operate.

In comparison, Linear Power, Ltd’s patented pressure actuation method simply uses pressure changes produced within shocks that dampen the end of the piston stroke, provide energy storage, and controls the length of the stroke. A pneumatic ram connected to a rack gear and pinion gear controls input of working fluid and exhaust to the pistons that is powered by the pressure changes within the shocks. The ram produces a back-and-forth motion of the rack gear in inverse relationship to the movement of the piston. The pressure actuation method allows rapid, continuous cycling of high-pressure working fluids without the need for electrical power or any external control sensors or controllers. The pressure change action takes place in real time relationship to the velocity of the piston and is regulated by the input volume and pressure of working fluid, which controls the number of piston strokes per minute.

Advantages of the “free-piston” engine include: (1) the high mechanical efficiency of a piston with reduced frictional losses, (2) elimination of the heavy crankshaft, which produces poor vector angles that cause inefficient power transfer to rotary motion and increases weight; and, (3) elimination of the need to compress air on the upstroke of the piston with the associated losses; and, (4) low initial and lifetime costs in maintenance (5) flexibility to harness the power of any kinetic energy resource without the need of a heat resource, such as the kinetic energy on natural gas wells and geo-pressurized water well, hydrostatic pressure for hydro-electric power, etc. (6) constructed to provide durability under extremely high pressures and within very harsh environments for improved operational flexibility, (7) high-power-to-weight ratio provides very high output power within a small area; and, (8) low noise and vibration as compared to turbine engines.

Power Sources and Uses
The Linear Power, Ltd free-piston engine can be used to perform any work for which any other engine many be employed, such as transportation, electric power generation, etc. However, we feel that our free-piston engine is uniquely the only engine that can be operated from oil and gas field geo-pressure with high efficiency.

Cost Effectiveness as Relates to Efficiency
From an investment point-of-view the important aspect of the technology is “cost effectiveness”, not the efficiency of the system. The thermal efficiency and mechanical efficiency of a power system along with system cost determines the cost effectiveness of a technology. One system can be twice as efficient as another system, but the other system may be four times less expensive; therefore, the less expensive system actually has double the cost effectiveness with the return on investment being twice as great for the less efficient system. Too much attention is given to efficiency, which is far less important to an investor than the cost effectiveness of the technology.

However, we have expended a lot of effort and capital to increase both the mechanical and the thermal efficiencies of our units. We have a new approach to getting more power from a heat source, especially low temperature heat sources, as compared to our competitors in the geothermal field that use the Organic Rankine Cycle (ORC). The additional power is attained through two means: (1) Operate the power cycle solely in the gaseous phase (sensible heat) requiring only a fraction as much heat energy to operate as compared to the Rankine Cycle utilizing phase change (latent heat). The ORC requires as much as ten times the heat energy input for latent heat phase change than does our proprietary hybrid Sterling / Brayton cycle, and (2) Development of a new proprietary hybrid Sterling / Brayton power cycle that provides both upper and lower temperature enhancement. The technology performs adiabatic compression of high enthalpy moist air to produce the heat-of-compression. Subsequent heat removal (the heat is used as the highest temperature of the power cycle) that causes condensation of the water vapor into liquid water that releases the latent heat during the phase change. The water is recycled to the evaporator. Then expansion of the cooled dried air produces very low-temperature air cycle refrigeration (the extremely cold air provides the lowest temperature of the power cycle) used to create a combined closed-loop evaporative cooling / air cycle cooling and low-temperature cycle refrigeration (for heat rejection) and condensation heating process that results in enhanced upper and lower temperatures for the power cycle, thereby producing a higher Carnot thermal efficiency for the power cycle from a low temperature heat resource.

Our low cost free-piston engine when taken together with our high mechanical and thermal efficiencies provides Linear Power, Ltd with cost effectiveness that is many times greater than that of our competitors.