Q&A



Q 1.  What is the maximum allowable H2O content in the fuel gas
The PowerGen employs a pre-mixed combustion system which can handle a significant amount of non-volatiles (i.e. N2/CO2/water content) as well as mixtures of non-standard fuels. It’s one limitation is actual liquids, as liquid buildup in the gas line will “plug” the gas line. As the liquid-saturation-point of H2O is a function of the mixture components as well as the pressure and temperature of the mixture, every site will result in a slightly different “H2O saturation” chart.

You will want however to prevent liquefaction and buildup of the entrained water as the gas goes thru pressure reduction in cold weather. Dropping pressure and dropping temperatures will push the H2O below its ‘Saturation Point’. To reduce this effect within the PowerGen fuel train we recommend supplying your fuel gas to the PowerGen unit at pressures of 5psi, and then install a simple, low-cost knock-out pot before our intake manifold. The KO pot will take care of the liquid dropping out of the mixture. Any other means to prevent actual liquids from getting in the fuel train are acceptable. Another way to further ensure that the H2O content stays in gaseous form is to provide an electrical heat-trace kit on the incoming gas line to prevent liquefication during cold weather conditions.

Q2 .  What are the maximum allowable solids content the fuel train can handle?
As mentioned above, the PowerGen employs a pre-mixed combustion system. The feedlines, as well as all the gas plumbing lines, are relatively large (i.e. we do not employ micro-orifices in the gas train).  Therefore the components in the gas train will not typically get ‘plugged’ due to the salt content. With this said, excessive salt and mineral content may begin to settle out and begin to build up within the various components of the fuel train.  In this case, the PowerGen would begin to experience a power reduction due to the constriction, causing a reduced fuel flow.  In this case, the salt/minerals would need to get cleaned out or the components replaced. The entire combustion system, as well as pre-mix burner, are designed to be field retrofittable. This means that if the excessive salt content is impacting the power generation level these components can be swapped out on a periodic basis.

Q3.   What is the heat loss through blower cabinet? i.e. how much heat is lost in the cabinet as air passes from the fan, past the plate/plate heat exchanger and then the radiator within the HRU?
The HRU (Heat Rejection Unit) is designed to reject the entire heat load of the generator, operating at full power, which is roughly 20kW of thermal heat (exact heat-rejection levels depend somewhat on ambient operating conditions). The Glycol Heat Trace module is designed to absorb up to roughly 18kW of this overall thermal heat from the main heat rejection loop and deliver it (in the form of heated glycol) to the customer application.

Q4.  Thermostat controls recommended hookup i.e. if the end-user needs to prioritize heat to a heat trace system, or their facility will go down. How would they ensure a certain inlet and outlet temperature into the glycol heat trace system?
Our master control system at this time is “electrical power led”. Meaning that the overall amount of heat generated is a derivative of the electrical power generation rate. The electric power level is set through the main user interface panel of the PowerGen. The more electrical power generated, the more overall heat generated. Once this heat is generated it can be delivered to either, the customer application in form of heated-glycol for heating the customer heat-trace system, or to the HRU to be rejected to the ambient air as reject heat. The ratio of heat provided to the customer via the Glycol Heat Trace (GHT) and/or rejected to the environment – is a function of the Return Temperature Setpoint on the GHT loop. The ‘Return Setpoint’ is our control parameter.  The PowerGen runs a control-loop on this ‘Return Temperature’ setpoint providing as much heat to the customer as required from the overall heat generated by the PowerGen (up to the maximum available) in order to maintain the user-defined ‘Return’ setpoint of the GHT. All the remaining heat, not used to maintain the GHT loop at the user-defined setpoint, is then rejected back to the environment. Reaching the setpoint in the GHT is prioritized, so all heat goes into the customer-loop until that loop is satisfied (ie. reached its setpoint).

 Q5.  Is it possible to use the same system at different well sites, but accommodate different power/heat demands, both per site and seasonally adjusted: i.e. how would the unit be re-prioritized for heat vs. electricity remotely, or is that a manual procedure?
The power level of the PowerGen is set by the user during commissioning. The power level is set at the max required the power of the greatest user (Electrical or Thermal). Meaning, if electrical power is the key deliverable then the power level will be set to the required power level. If however only a small amount of electrical power is needed and yet significant thermal power is required, the PowerGen will be set to generate an electrical level corresponding to the required thermal power. This power parameter is easily set on the PowerGen and can be tuned so each site has sufficient electrical and thermal power to meet its needs. All electrical power produced that is not consumed by the customer loads is converted into heat and is provided to the customer as overall available heat. Units with the GHT loop feature option added will have most of that heat available for on-site heat duties. Those sites or applications which do not use this heat will find that the HRU (Heat Rejection Unit) is sized to reject waste heat for a very broad range of temperatures The PowerGen HRU is sized and tested to keep the PowerGen functional in ambient temperatures as high as 50C.

 Q6.  What is the inrush current capability?
The PowerGen has (x2) electric power outputs, both outputs are rated to 23.5 Ampères of AC current each. We typically provide customers a 240VAC/120VAC split-architecture, which is similar to standard residential utility supply. This means that output A is at 120VAC and output B is at 120VAC. The two outputs are synced and at 180 degrees out-of-phase with each other to provide 240VAC across them. For 24VDC loads, we recommend using our battery charger/tender solution which provides 3-stage battery charging and float for ensuring battery health and longer life. The standard chargers we use come in sizes ranging from 20ADC up thru 45ADC. Larger DC-current solutions are available up to 160A on special request.

Q 7.  Heat Tracing: Do we have delta T info on the glycol heat trace loop specifically for a variety of temperatures, and
Please see attached GHT brochure, specifically the chart on page 2/2 for temperature and power output at return set points.

Q 8. Is 1500′ the total length of the heat loop?

The heat trace loop is sized to be 750’ each way for a total 1,500’ length. We have tested the PowerGen across multiple line lengths and temperatures conditions. This includes testing at field locations on GHT loops of up to 1500’ ft. The pump we use is actually rated to push glycol (at STP conditions) through up to 1800 ft’ of 1/2” SST pipe. All our sizing is based on 1/2” SST piping.

Q9.   Is it a different set of parameters, such as delta T in and out in a specific situation?
The Return Setpoint can be set by the user and is therefore specific to each situation.
The ‘Inlet Temperature’ into the Glycol Heat Trace system accessory on the PowerGen can be above 75 degrees Celcius but modulates, as required, to fulfill the user-defined ‘Return Temperature’ setpoint.

Q10.  What happens to power right after shut down?  i.e. does the electricity immediately stop flowing upon shutdown, or does load slowly diminish while unit powers down?
In an ‘Emergency Shutdown,’ the electric outputs are immediately disconnected and the generator is shut-down in a safe, but a rapid way. In standard operating conditions of normal On/Off operation there is a transient period in which the combustion system turns off and then the generator begins to cool until it eventually shuts off. While cooling, the unit will continue to produce some power until it completely shuts down (i.e. pistons stops moving). In a standard shut-down procedure the PowerGen will typically continue generating electricity for roughly  1-2 minutes from giving the shutdown command.

Q11: How is this specific Stirling Engine designed for no engine maintenance?

A:

  • No linkage
  • No oil or lubricants
  • No friction
  • Helium-filled at commissioning
  • No moving parts with mechanical linkages
  • Bending part:  Flexure springs – Tested beyond 1 billion cycles with NO failures

Q12: How does PowerGen efficiently produce variable power outputs?

A: A dual magnetic field on our integral linear alternator allows split or combined outputs of same or different voltages in one system.

Q13: How is this specific Stirling Engine designed for no engine maintenance?
A:
• No linkage
• No oil or lubricants
• No friction
• Helium-filled at commissioning
• No moving parts with mechanical linkages
• Bending part: Flexure springs – Tested beyond 1 billion cycles with NO failures

Q14: How does PowerGen efficiently produce variable power outputs?
A: A dual magnetic field on our integral linear alternator allows split or combined outputs of same or different voltages in one system.

If we are starting, say a 10HP motor across the line, would two 5.65kW units in parallel be able to handle the starting current?
For highly-inductive loads (like electric motors) we couple the PowerGen to an appropriate drive which reduces the issue of in-rush.

Q15:If the motor is on VFD, do we need to worry about harmonics?
As mentioned in #1 we recommend powering electric motor loads with a VFD. In our testing on such loads (while using a VFD) we have not encountered issues with harmonics. Whatever the case, we always pre-test and validate each VFD + motor load application here at Qnergy, prior to approving for customer use.

Q16: With units running in parallel, how is the load sharing done among them?
When paralleling PowerGens we have the option to output the produced electrical power to a common High-Voltage DC (HVDC) bus. The power controller of each PowerGen unit regulates the electrical output of each PowerGen to maintain the desired “common” HVDC bus voltage. By paralleling multiple units like this on a single HVDC bus allows us to maintain a stable high voltage feedline which we couple to a VFD, inverter, or other.
Q17: Are the units able to put out 480V, 3 phase?
We have tested electrical motors running 480V, 3-phase (using VFDs).

Q18: Are the units able to put out 600V, 3 phase?
The PowerGen can support 600Vdc (not AC). In this case, we would couple to the electrical load via a drive or inverter. If provide details on your specific load and operating profile, we can specify a recommended solution.

Q19:

1. What can I power with PowerGen?
a. A: AC electric motors up to X HP three phase
b. A: AC electric motors up to X HP single phase
c. A: Glycol heat tracing systems up to 1,500’ (approx. 500 meters) long
d. A: fan-powered heaters such as Ruffneck building heaters.
e. Electrical heat tracing in a variety of configurations
f. Any system up to X Amperes. PowerGen is capable of handling two circuits up to 20 Amperes and a total of

5,650 Watts and a second PowerGen generation is now available in X Ampere and 1,200 Watt Configurations.
What electrical configurations are possible with PowerGen?
a. Insert 6 different standard configurations in brochure here.

How does PowerGen adapt to fuel variations?

Q20: How does PowerGen deal with operating outside design parameters?
a. A: control and automatic shutdown features in place

Q21: How is PowerGen output affected in cold weather?
a. A: PowerGen becomes increasingly efficient in cold weather, but is designed and tested to work in temperatures as high as 50C ambient.
Does Powergen have the ability to provide AC as well as DC
a. A: PowerGen is capable of providing a mix of any and all of 12 and 24VDC as well as 120, 240 and 360VAC

Q22: Is PowerGen noisy in operation?
a. A: PowerGen is so quiet you can have a normal volume conversation while it’s in operation. Sound levels of around 70dB are typical.

Q23: What fuel composition can PowerGen accommodate?
a. A: PowerGen is capable of handling BTU values as low as X and as high as Y.

Q24: How adaptable is PowerGen’s to fuel contaminants?
a. A: PowerGen requires fuel in the form of liquids-free gas. However, it can handle as much as 1,000 ppm of H2S in the fuel supply.
What are emissions like for PowerGen?
a. NOX levels

Q25: What is the efficiency of PowerGen compared to other forms of power Generation
a. A: Powergen is X times more efficient than an internal combustion engine. PowerGen is between X and Y times more efficient than fuel cells , and PowerGen is between X and Y times more efficient than TEGs. This is because PowerGen has the built-in ability to efficiently control its blower-assisted air/fuel mixture.

Q26: How is PowerGen’s ability to adapt to external temperature changes
a. A: PowerGen is configurable to a variety of environmental and duty-related ambient conditions from -40C to +50C.

Q27: What is PowerGen’s compatibility when tying multiple units together in series or parallel
a. A: PowerGen is pre-configured to easily tie multiple units together so that little is required in terms of field connections.

Q28: What is turndown like for the Powergen?
a. A: PowerGen can be turned down as much as 50% and still operate well within design parameters.
b. A: PowerGen is capable of maintaining full functionality even when no power is drawn from the unit. It is capable of reducing its own operating load and at the same time, it can manage its internal systems to continue to run by loading its cooling system during low demand periods, without ill effects on the overall system. The PowerGen is designed for adaptability to convenient remotely controlled stop/start as well as long-term critical power providing operations.

Q29: What is the remote monitoring capability of the unit itself
a. A: PowerGen comes with a free X month connection to it’s in-house developed remote monitoring system which provides

Q30: Is PowerGen certified for use in Canada and the USA?
A. Electrical code compliance was part of the PowerGen development program from the onset. PowerGen is certified by Intertek to comply with these regulations X, Y, C.

Q30: What industry sectors use this technology?
a. Oil and gas
b. Pipelines
c. Communications
d. Air transportation and navigation
e. Rail
f. Domestic
g. Naval power and navigation
h. Agriculture and dairy
i. Cryptocurrency miners
j. Medical cannabis growing operations

Q31 What happens internally if the air intake was to suck in an air/gas mixture?

A: Powergen is tuned to operate lean- access fuel of around 3.5-4% O2. Adding fuel into the intake air will, in turn, reduce the oxygen content, causing a rise in the flame temperature until it becomes too rich, causing incomplete combustion and high levels of carbon monoxide. The Powergen monitors its engine head temperature and will lower the burner rate when the head over-heats. Therefore there is no risk to the hardware. In all cases, the flame remains inside the combustion chamber and is not capable of traveling upstream beyond the quenching plate (perforated plate behind the burner deck). Burner chamber volume is sized so that the flame cannot exit and travel down the sealed exhaust ducting, therefore no exposed flame.

Supporting illustration:

Q32  Can this generator as a whole ignite external flammable gases?

In other words, should you treat the PowerGen as open flame equipment, which impact its location on the site due to spacing requirements of this type of equipment?

Answer:

The Qnergy PowerGen 5650 has an enclosed combustion chamber that is fully encapsulated within heat exchangers in such a way that there is no exposed heated surface hot enough that could cause pre-ignition to external air-borne flammable natural gas.

In terms of ingress of externalair-borne gas via the exhaust system into the combustion chamber, we have apositive pressure combustion chamber which, when the unit is operating, preventsany ‘unintended’ flammable gas access to the combustion chamber.

To help you with locating the PowerGen on your site, we have further clarification from Alberta’s EnergyRegulator: “Given how the Sterling engine operates, with an enclosed combustion chamber and no possible way for a flame front to exit the unit if an air/gas mixture is drawn in, I conclude that it operates more like an internal combustion engine rather than flame type equipment.” (June 25, 2018)

Q:33 The PowerGen is capable ofburning sour fuel gas with up to 1,000 ppm H2S; Will we be requiredto do dispersion modelling?

Answer:

Section 7.12(1) of (Alberta Energy Regulator) AER Directive 060 requires dispersion modelling if the H2S content is greater than or equal to 10 mol/kmol (your 1000 ppm would be 1 mol/kmol) or one tonne per day.  PowerGen doesn’t trigger either of these, so dispersion modelling would not be required by Directive 060.

Note that our free-standing height is only 54 inches, so it would be possible for the emissions to be very undispersed if someone was standing nearby. OilPro recommends consideration is given to determine whether the operator might want some sort of setback distance so that a person couldn’t stand too close to the exhaust.

The heat of the exhaust will provide some lift and may act like an effective stack height, taking the plume up into the air, to then disperse more as it travels downwind. The Air Quality Objective for SO2 is 172 ppb, so the dispersion would need to be taken from the original concentration of about 1,000,000 ppb (1,000 ppm) resulting from the original 1,000 ppm of H2S, down to 172 ppb.  Dispersion is quite effective, so this is probably not difficult to achieve (comparatively much larger sources still dilute to levels below 172 ppb), but if required it is recommended to model the scenario to be sure of each case.

Bottom line: no, AER requirements do not require a model of the gas stream of this low H2S concentration and rate.

Q: What makes the Free Piston Sterling Engine (FPSE) last so long without maintenance?

Answer: For the in-depth version, visit https://www.spaceflightinsider.com/space-centers/glenn-research-center/it-keeps-going-and-going-stirling-engine-test-sets-long-duration-record-at-nasa-glenn/, which explains NASA’s experiment with the FPSE which has been running continuously since 2003. Only maintenance of monitoring instruments and component inspections have interrupted the continuous duty of this engine.

In brief: The FPSE is designed to have no contact between moving parts. There are no contacting bearings or seals which eliminates wear items. Secondly the hot-end metallurgy, weld procedures and assembly methods were carefully chosen for their durability. Any engineer will tell you that the best designs are usually the simplest. The FPSE is no exception. The engine contains helium gas, which is heated at one end, and as the helium expands it forces a piston away from the hot end and into an oscillating cycle. Indirect action between this piston induces movement of a secondary piston which incorporates a linear alternator that generates electrical output. There is no rotary motion, no crank, just back and forth movement, enabled by internal springs called flexure plates, which resemble the small discs found in 45 RPM vinyl records. The flexure plates are designed around a material fatigue life beyond that of the required operating life of the engine. The engine design life is in the order of 10-20 years to match NASA’s mission durations in the 17-year range, but speculations indicate these engines can last beyond 20 years. We’ll only know for sure in 2023.

Q: Why should we consider the PowerGen a clean technology when it burns hydrocarbons?

A: This comes down to what Ory Zik, CEO of Qnergy calls “Carbon Literacy”, which involves taking into account a system’s overall lifetime carbon footprint https://www.youtube.com/watch?v=r77z4zsTT64 . There are four reasons the PowerGen should be considered to have a lower carbon footprint versus alternate remote site critical power generation systems.

First is the lifetime carbon footprint.  We must take into account the total lifetime carbon footprint of an engine. The FPSE was declared by NASA to be “the most reliable generation technology in history”.  The FPSE requires minimal scheduled maintenance and component replacement/service. No oil changes and fewer visits to PowerGen sites mean less carbon-intensive maintenance. This is why the PowerGen compares favourably versus internal combustion engines but als compared to fuel cells, both of which require replacement of major components at regular intervals.

Second is the efficiency, either stand-alone but also in a CoGen application. Consider the PowerGen’s ability to control combustion at a near-perfect stoichiometric ratio, once installed, regardless of the fuel gas quality used. This means there is an extremely efficient conversion of the energy in the gas being burned to electricity and heat. This is achieved with the use of an air-assisted on-board system-powered blower which is adjusted to match the burner’s need for air with the BTU’s available in the fuel gas. In colder climates Co-generation plays a role. In applications where a continuously maintained process temperature is important, the PowerGen provides additional carbon footprint reductions by using its own waste heat to circulate hot glycol on site. This raises the PowerGen’s overall efficiency from the roughly 20-30%+ range into the 70-80% range. Converting energy on site using gas available on-site fuel is extremely efficient. When you consider that fuels such as gasoline, diesel or processed gas can ultimately result in an overall energy conversion rate in the 10-20% range at the driven wheel of an automobile after all the losses throughout the processing and distribution networks, decentralized power generation makes a lot of sense. Similar losses apply to centrally generated and distributed electricity networks, regardless of the means used to generate power, due to line losses in distribution.

Third is the reduced reliance on backup battery storage. The Powergen, due to its significant power output compared to conventional remote power sources like ThermoElectric Generators (which, like the FPSE are a very reliable form of heat engine, but only due to their relatively short conductive path, end up converting only 6% of that heat into electricity) and fuel cells (Which can be both fuel dependent and have a limited, expensive, key component lifespan), means fewer backup batteries are required because the PowerGen can help recover drained onsite energy storage more quickly. As the charge rate is much higher, lower reserves are required. Solar and wind power require even more battery backup due to their intermittent and seasonally variable nature. We all know that our car batteries eventually die, with a typical lifespan of 2-5 years. Reducing the amount of required backup power causes a significant reduction in the carbon footprint of the overall system PowerGen is part of. PowerGen customers are also using the Glycol Heat Trace (GHT) option to keep batteries within their most efficient temperature range, further extending battery life and reducing the need for additional backup in low temperature operations.

Fourth is that the PowerGen shines at times when everything else on a site starts to fail.  The PowerGen becomes more efficient the colder the ambient temperatures are, which happens to coincide with PowerGen customer’s greatest reliance on continued operation of their facilities. During the prolonged cold spell of the 2019 Polar Vortex which saw temperatures dip into the -30C bracket, OilPro’s PowerGen customers reported how pleased they are that many cold-related site visits related to freeze-up problems were eliminated due to the system’s increased reliability. Fewer emergency shut-downs mean fewer unscheduled site visits, which means fewer hydrocarbons burned calling in men, trucks, steaming equipment for unscheduled visits.

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