A “tomato digester”, (a tomato grower's greenhouse waste AD plant) and how “Complete Idiots” built it, is a story of success. How, from being, (in their own words) “idiots” grappling with biogas technology, they consistently applied the operating experience to plant improvement and expansion. And now, are at the point where AD provides a financially secure foundation for their family business.
It is easy to forget that only a short 15 years ago the biogas industry was far less developed than it is now in 2022.
Back in 2007, if you wanted a non-standard digester tailored to anything other than an agricultural feedstock, such as dairy farm manure, or maize crops, you were pretty much on your own.
Many said that anaerobic digestion was not a proven technology. They said that it was very expensive, unreliable, and risky to invest in anything like a tomato digester. In fact, if you listened to the consensus of opinion for most people in those days was that only “complete idiots” would ever wish to build a tomato digester!
Read on, below, and decide for yourself whether these guys were either tomato digester idiots or well ahead of the curve:
Press Release August 2022:
Being Complete Idiots Building Our Own AD Plant
On the website of tomato producer Guy & Wright (established 1928), the company describes itself as: ‘being complete idiots; building our own AD plant’.
Fifteen years ago, when the first 1800m3 tomato digester was built on the 100-acre site in Hertfordshire, England, John Jones (great-grandson of Mr. Guy) could be forgiven for wondering what on earth he’d taken on!
As if producing hundreds of tons of top-quality tomatoes each year wasn’t enough to think about, he was now getting to grips with a very steep biogas learning curve to understand:
- how to optimise the rate of digestion of his feedstocks,
- set the best tomato digester reactor temperatures, and
- make the best use of the resulting digestate.
So, was their tomato digester worth the heartache?
A decade and a half on, with a second, 7,000m3 digester, no energy bills, and enough excess power to sell for the equivalent of 1500 homes, Guy & Wright are a shining example of how to survive and thrive through diversification into renewable energy.
These “Complete Idiots” were Doing Well even Before Rising Energy Prices Struck in 2021
None of us could have predicted the sudden, massive leap in energy prices that are such a challenge today. But even in the early 2000s, rising fuel costs were already a big concern for John Jones. In the heat-thirsty business of producing tomatoes in the UK climate, he knew even back in those days, that he had to act decisively in order to:
- reduce costs in an increasingly competitive UK tomato market as the only way to
- protect and develop the family business.
Step 1 – Avoiding the Rising Cost of Electricity While the Supply of Non-renewable Natural Gas was Plentiful
At first, five natural-gas-powered 115kW micro-turbines were installed to produce hot water, electricity, and CO2 for their tomato-growing greenhouse operation. At first, all went well with that, but before long, with natural gas prices rising steeply, Guy & Wright began to look for ways to reduce their energy costs.
Step 2 – Using their Own Organic Waste as an Energy Source
Creating biogas from the tomato crop waste seemed to make sense, but would it work?
It seemed like a risky venture. Nevertheless, they soon reached the point of no return, when they invested in a 500kW CHP (combined heat and power) engine from Edina; converting three of the five turbines to run on biogas.
Step 3 – Making Good Use of a “ROCS Scheme” Subsidy
This action enabled Guy & Wright to apply for ROCs (Renewable Obligation Certificates). These were a form of government subsidy at the time (since discontinued).
They allowed the generators of renewable energy to sell on and receive a premium payment, in addition to receiving the wholesale electricity price.
Step 4 – Applying Börger's Specialist Pumping and Digestate Separation Equipment Technology
The investment in carefully-sourced equipment also saw the start of what has become a long and productive relationship with Börger; best known for its rotary lobe pumps, but also makers of key farming/biogas kit.
In 2008, a Börger Multi-crusher was put into operation to reduce feedstock particles down to 8mm to enhance the AD process. One might expect there to be no shortage of waste from growing so many tomatoes, but John Jones’ son, Rob, who now runs the biogas operation, soon saw that tomato leaves were not only extremely difficult to break down, but also low in calorific value.
So, as the never-ending fine-tuning of the AD plant continues. Locally imported waste now includes:
- citrus fruits,
- grain, and
- cocoa powder
- plus processed DAF sludge from an ice cream manufacturer.
This last item provides liquid to help create a ‘milkshake’ consistency that the digesters will benefit from far more than a consistent supply of more solid material.
“The Börger Multi-crusher certainly proves itself as a very durable and effective piece of kit for the demands of an AD plant”
, said Rob Jones.
“We keep one Multi-crusher as a spare so that in any eventuality, we can keep operating – with two always on the go, plus an additional unit now on order. They work very well for us”.
Börger Rotary Lobe Pump
Based on the proven Börger Rotary Lobe Pump, the Multi-crusher chops coarse material ahead of delivery to the tomato digester reactor tank to ensure that downstream machines and pumps operate smoothly. The Multi-crusher homogenizes mediums at throughput volumes of up to 320 m³/h / 1,400 USgpm/h.
In addition to food waste, it can handle fibers, pieces of wood, plastics, membranes, and textiles across a wide range of applications.
The team at Guy & Wright added:
“Investing in our first CHP was a real turning point, and as we’ve grown the biogas plant, converting (covering) our old lagoon into a secondary, 7000m3 digester*, we’ve not hesitated to invest in more Multi-crushers from Börger”.
Guy & Wright secured another Börger Multi-crusher when it began taking in liquid animal bi-products, for which they also needed a (7.5kW) Börger pump. Utilising this type of bi-product (via a new pasteurizer) has provided another important string to the Guy & Wright bow, enhancing biogas yields by having a feedstock with a high calorific value and also less digestate to deal with.
Biomass Boilers Added to Tomato Digesters
Two biomass boilers are also now in the fleet of machinery, providing much-needed additional heat to the nursery during winter. Hot water is stored in a buffer tank so that it can be used on demand. Guy & Wright has also become the first company in the biogas industry to take exhaust gas from a CHP and convert it into CO2 for the glasshouses.
The gas is cleaned by a special system of catalyst bricks that absorb harmful gases; leaving the resulting CO2 (which is piped into the glasshouses) at perfectly safe levels. This also aids the photosynthesis of the tomatoes, resulting in more plentiful flowers/fruits.*
‘Success with new Börger Separator’
Börger Bioselect Separator Added
Always looking for improvements to their tomato digester, Guy & Wright turned to Börger again to address the dwindling capacity of the plant’s open lagoon. Working together with four nearby farms, there had been problems with blockages during spreading with an umbilical system, but that’s all changed for the better now, thanks to the purchase of a Börger Bioselect Separator.
Using a purely mechanical process, the liquid is separated from the solids in the medium, so that nutrient-rich organic matter (PAS 110-approved at a maximum of 2mm) can go back to the land as a top-quality crop fertiliser.
With a combination of a separation machine and two Börger Rotary Lobe Pumps (www.boerger.com), the Separator is load-triggered. The feed pump only conveys to the tomato digester the volume that the Bioselect is able to process. The high-density solids discharge pump determines the degree of thickness.
“We no longer lose capacity in our lagoon”, concluded the team at Guy & Wright. “This is due totally to the Börger Separator, which protects it. Works an absolute treat”.