We started our first biodigester in April 2022, and the second one came online in September 2022, It took a while for them to adjust and start producing methane in reasonable quantity, mainly because we had to learn how to manage our biomass. Thanks to Eric and Jeremy, respectively our ecologist and biologist, we have been tweaking the input to increase winter gas production. In effect, we have to ensure that the biodigester is more performant during the winter. The improvement is achieved by adding certain metals (trace), accelerants, and various biological additives, including alkali solutions. This is very complex and is entirely driven by the initial composition of the waste and its moisture. In a nutshell, it's an ever-changing chemical analysis that dictates what is added to improve performance.
Every 18 months our biodigesters are thoroughly inspected. Our primary concern is rust, biogas are "wet" and they can easily damage processing equipment. The brother of our biologist, who is a petroleum engineer, visited the farm when we were building the units, and suggested that we choose a higher-output gas dryer. He said the additional cost and energy usage will be more than paid back by equipment longevity. Our most recent maintenance review seems to confirm this, with almost no rust in the systems.
The first unit was inspected in the late spring of 2023, the inspection needed to be completed before the warm weather to make the most of the summer heat for re-starting the digestor. Our two units are by far the more complex systems on the farm, as they not only produce biogas but also create our compost, and treat our wastewater. The magic is the gas separation, compression and sequestration all well-understood, and mature technologies. What has been amazing is that our biologist has been able to "tweak the manure input to maximize system efficiency.
A few days ago we received all the spare parts for the biodigestor that had been ordered by the maintenance and inspection company. None of the components were urgent, and there was far less wear and tear than anticipated, but some parts are "cycle specific" and these will need to be replaced early in the spring (in about 12 weeks the maintenance company will be coming back to replace these parts when they do their annual inspection on the first biodigester).
When the maintenance company did the inspection of the first biodigester and its systems I asked them if they were concerned with supply lines for Chinese systems (like ours) they told me that almost everything could be modified if the parts were no longer available from China.
Our system is unusual. We have two biodigesters and two generators but only one gas treatment plant. The gas output is compressed and stored in tanks near the biodigesters and twice a week or when the feed tanks are full, the gas is processed and stored in the appropriate tanks. As an example, on Monday, our team of mechanics started the transfer and processing of combined gases, it takes 8 hours to process all the gas feedstock so that it can be split and dried.
The tanks that have the most rust are those initial tanks, they are only rated to last five years. Then inspected by a specialized firm for wall thickness. There's an entire certification process -- again that's something that the inspection team completes (it's like a car really).
I mention all this because it is important to understand that like every complex system, our biodigeters require inspection and maintenance. Economically, biodigesters are great when LPG is expensive (it's not that bad now). For us, the real feature is that it transforms a variable cost into a fixed cost. Energy is one of the three most important variable costs on a farm. We can afford to take the view that LPG prices will rise rather than decline. Based on current prices (which are more or less at the historical average) our Biodigester will become "free" in seven years. If LPG prices double, then it's three years, and if like in 2022 when the price of LPG spiked sevenfold, then it's one year.
Note: I had a question about CO2 additive to our high tunnels, and why we do that. Basically, plants absorb CO2 during photosynthesis (aka daytime). At 6 am we turn on either our blue (400 – 520 nanometer) or red lights (610 – 720 spectrum range) to promote either growth or flowering. We add CO2 after picking is ended, and we shut the gas down when we turn these lights off (around 8 pm). This represents a very small increase in the overall level of CO2 but has a huge impact on the growth performance (we think about 40%). We use the lights because the polycarbonate that covers our high tunnels filters about half of both frequencies. We also use the CO2, like the lights to slow down the growth rate of plants in certain high tunnels so that our production better matches our customer demand. By far the biggest advantage of high tunnels.
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