Iâ€™m in the process of designing a simple 3kW steam engine for both a combined heat-and-power gasifier system and our solar power generator system. I canâ€™t help but think about the future possibility of small-scale steam power for both stationary and mobile steam power applications.
In absence of a really suitable open source 3D CAD program, I downloaded a free trial version of Alibre Design Xpress 3D solid modeling software – to do a basic 3D model of the engine we’re building, for which we have a $250 bill of materials:
The basic concept is – as mentioned in a previous post – a high performance modern steam engine of 20% efficiency can be made without much technical difficulty. Remember that our present solar turbine design requires only 5% efficiency to become feasible.
Moreover, a simple direct coupling of the steam engine to a linear hydraulic pump –
means that you have a super-simple hydraulic power source for devices like our open source tractor, LifeTrac. This brings LifeTrac much closer to the reality of being powered by high performance, modern steam – via local production. As such, LifeTrac would become integrated into the local agricultural ecology – capable of being powered by a gasifier or pyrolysis oil from local biomass.
Now I’m busy on the standard steam engine of the 3D drawing above – so if you want to see the latter hydraulic pump hybrid come to reality sooner rather than later – contact us right now and let’s start talking about fabrication. By the way, there is a resurgence of interest in such hydraulic drive in the mainstream economy.
Stationary biomass power in most temperate areas has a lot of potential and can be quite sustainable if done properly. In particular I am attracted to the idea of developing a fully integrated gasifier, flash boiler, steam electrical generator. The design could be broken done into three different processes.
- Combustion: Combustion would be done in a two-stage process known as gasification. In the first stage a minimal amount of air and heat are combined to generate wood gas, in the second stage a full amount of air is delivered and combustion is completed. This process is cleaner and has the added benefit of generating a char that is much higher in carbon an is claimed to be highly beneficial for soil.
- Steam Generation: The next stage is where heat is transferred from combustion to the flash boiler. Here the hot portion of the flame is in close proximity to the end of the monotube flash boiler and produces high temp steam. As the combustion air is driven up and out it passes over the incoming tubes and warms the water before it is heated into steam.
- Steam Power conversion: The last main process occurs in the steam engine, here the steam is expanded against a cylinder which is driving a generator AC or DC or else doing mechanical work. The steam is then exhausted into the condenser. The condenser is also a large 500-1000gallon thermal storage tank for hot water and space heat. Finally the condensed steam is pump as water back into the monotube flash boiler to go through another cycle.
Here is a diagram of the process I am proposing.
In summary with the cogeneration of electricity or mechanical work and heat all energy from the biomass is used. Additionally the clean combustion process produces little to no emissions typical of biomass combustion and furthermore even produces a very useful agricultural component known as biochar.
For mobile applications I believe steam may also be due for a renaissance. It is well documented that 1920 steam engine vehicles often beat their gas counterparts in emissions, acceleration, and equaled them on fuel economy. Much less known is that they also were the first vehicle to be driven off of solar thermal energy. In 1915 an inventive Dr. Robert McEleroy used a tank of refinery byproduct to store heat at 900 degrees, from a heat exchanger he was able to produce steam to travel up to 35 miles with his vehicle. So steam does have an interesting vehicle power history, particularly before well refined petrol products arrived (a condition necessary for the internal combustion engine to survive).
So here is an idea I would like to bounce off all creative minds out there. Right now hydraulic hybrid vehicles are receiving a lot of attention as efficient drivetrain choices. One advantage is that the pump can be tuned backwards against a high-pressure accumulator for regenerative braking additionally there is no longer a need for a transmission. So given the advantages of hydraulic drivelines in vehicles and machinery why not design a free piston steam hydraulic pump. In concept it might look like this.
The concept would be quite simple; steam is expanded against a hydraulic cylinder which stores energy in a high pressure accumulator. As the steam loses pressure due to expansion the hydraulic cylinder forces slow the cylinder, by the time the steam cylinder uncovers the exhaust port the steam cylinder is nearly stopped and the pressure on the hydraulic cylinder accelerates the steam cylinder back towards the steam inlet port. Steam is then admitted by either an electronic solenoid valve or a mechanical valve and the cycle starts again. There would also need to be two check valves arranged as shown in the diagram to allow the hydraulic fluid to enter the cylinder from the low-pressure accumulator and also to provide a route back for hydraulic fluid on the compression stroke.
If this simple engine proves itself in concept it seems like a potentially ideal candidate for mobile hydraulic applications both on and off road. It would be mechanically simple, capable of storing some energy for intermittent power bursts (acceleration, initial pulling efforts, ect) and because of lack of crank and block it would have a very high power to weight ratio. Mobile steam power for the 21st century? Weâ€™ll seeâ€¦.