Power Bytes

Waste to Energy: The BioGas Story

September 01, 2021 Caterpillar Inc. Season 2 Episode 10
Power Bytes
Waste to Energy: The BioGas Story
Show Notes Transcript

Renewable power generation, decarbonization and the energy transition are very hot topics right now.   As we continue our focus on fuels, we wanted to highlight one of particular importance both from a use case scenario and to its completely sustainable nature.  That fuel is biogas.  From Geneva Switzerland we are joined by Sven Buhler. 
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Lou:  Good Day and welcome everyone to Power Bytes!  I am your host Lou Signorelli and Power Bytes is your destination Podcast for power generation discussions.  As always please know how much we appreciate you, our listeners.  We hope you find our topics helpful and interesting.  There are several ways for you to get in touch with the show. You can send us an email at powerbytes@cat.com, visit us at Cat Electric Power on Facebook or LinkedIn.  Please remember to subscribe if you enjoy your time with us today. 

Lou: Renewable power generation, decarbonization and the energy transition are very hot topics right now, and topics that we've touched on recently as part of our focus on fuels. 

As we continue our focus on fuels, we wanted to highlight one of particular importance both from a use case scenario and to its completely sustainable nature.  That fuel is biogas.  

Lou: Joining me today via the Cat Electric Power Hotline, from his home office in Geneva, Switzerland is Sven Buhler. Sven has a Masters degree in Mechanical engineering from the Swiss Institute of Technology and 20 years of experience in power generation. After starting his career working as a R&D engineer for gas turbines, he joined Caterpillar and spent the last 16 years in Electric Power serving in the sales of prime power products and bespoke power solutions. Sven served the last 8 years as sales representative for Large Electric Power Gas products. 

Welcome to Power Bytes Sven, we are glad you're here.

Sven: Hello Lou, great to be here !

Lou: When I think about biogas I'm impressed by both its sources and many benefits,  most significantly the reduction of harmful methane gas emissions. From animal waste, crops, waste water and even food waste, it seems biogas can be derived from anything organic.  "Sven" what is biogas exactly?

You are right Lou, as Biogas is a mixture of gases, produced by degradation of organic materials and it can be derived from several types of feedstock such agricultural waste, municipal waste, sewage, food waste. The beauty is to use this organic waste to create a renewable energy ! 

The typical agriculture substrates can be energy crops such as maize silage, sugar cane, cassava or other waste like manure, harvest residue or a mix of these. In municipal waste we will find sewage sludge, grass clipping or food residue. From the industrial sector, biogas can be produced from food & beverage, dairy, starch and sugar industry. Slaughterhouses, pharmaceutical, are also good candidates. Hence biogas can use a wide range of organic wastes thus has a great potential ! 
Depending on the material used the biogas yield and methane content will vary and therefore energy output as well.    

Lou: And how does it become biogas from these different sources?  What is the process?

Well biogas is a by-product from the process of anaerobic digestion (which is similar to human digestion).  This process consists of a series of steps during which the material is fed to the digester where different micro-organisms are at work and in the last stage, bacterias such as methanogens, produce a gas composed of mainly methane and CO2 ! The sludge that remain is rich in nutrients and can be used as a fertilizer. At the start one has to consider what local wastes are available, different methane yields to select suitable digester. 

Lou: It was not too long ago and probably to a lesser extent today, we might just have seen these gasses released into the atmosphere, or even Flared. I remember seeing flares on landfills this driving along the highway as a child. I understand we can use this biogas today as a fuel?

Sven: That's right Lou. We can and we should ! As biogas contains methane, which has a strong greenhouse potential it is key to use it ! Flares are part of a biogas plant equipment but should only be used to prevent the gas to escape if it cannot be used due to maintenance work, or very poor biogas quality. Unfortunately in some locations these biogases are flared off due to lack of finance or incentives or in landfills biogas escapes to the atmosphere due to improper site design and management. The goal of waste-to-energy applications though is to capture the gas, refine it and use it for example in gas generators where it's converted to useful energy. 

Lou: What are some of the most prevalent uses of biogas fuel?

Sven: Biogas can be used in several ways. One path is to produce biomethane which is a purified biogas after removal of CO2, H2S and moisture. Biomethane is then injected into national gas pipeline to be used by the gas consumers for their typical use like heating or in Combined Heat and Power application. Biomethane is a renewable gas and displaces use of fossil fuel like natural gas and is compatible with our CAT gas engines. 

Of course biogas can be used directly as a fuel to power gas generator sets providing renewable power and heat. Thanks to on site power production, it enhances the site resilience towards grid outage and reduces its reliance on local electricity purchase. In most cases Biogas installations include a Combined Heat & Power Solution which exploits the waste heat of the genset. This heat can be applied to AD to support production of the biogas but can also be used to replace heat production from nearby coal/oil fired boilers to supply hot water for example. Thus energy efficiency of the process is increased substantially and displaces fossil fuel. 

Lou: Could you share some project examples ? 

Sure and we have several but let's have a look at the example of the Gab-El-Asfar Waste Water treatment Plant in Egypt. Thanks to a total capacity of 2.5 million cubic meters of waste water everyday it is the largest in Africa & the Middle East ! Processing this volume of waste water requires a large power consumption which represents a significant utility cost to the operator. Customer selected Cat CG260-16 genset due to the product high efficiency, low operating cost and local service capability. In this power plant the biogas is converted into 16MW of power which covers 80% of the plant's own power requirements! 

Lou: Wow ! That's a huge example - is biogas accessible/feasible to smaller businesses?

Sure we have a perfect example of one site which has grown over time and is perfectly integrated in the nearby community. This site is located in Belgium and collects waste from different sources such as nearby agricultural (maize, manure, rye, grass silage, etc), food processing industries waste (sewage sludge, food wastes), local communities mowed grass. At the start, the  site had enough biogas to feed 1 x 600kWe unit and today, the waste collected amounts to 50'000 tons which is then fed to the AD plant to produces 
 • 700m3/h of biogas, so enough to produce approx 1,5MW electrical output which represents approx. 6000 homes. 
 • The heat recovered is used to maintain digester at appropriate temperature, but also to dry the wood residue which is compacted & used in home stoves 
 • Finally the digester residue is also valued and used as fertilizer by local farmers to support crop growth 

Hence a perfect example of circular economy ! 

Lou: When a business contemplates using biogas, what are some of the considerations they need to take into account when using this fuel?  Are there any special handling or maintenance considerations?

Sven: A biogas plant consists of a number of elements like the Anaerobic digester for gas production, gas treatment components, and the energy conversion unit through gas generator sets and CHP system. This part is a key piece and as explained Biogas is composed mainly of CH4 and CO2 but also contains moisture and traces of hydrogen sulfide (H2S) or siloxane or other corrosive substances . In regard to the genset and CHP system the key considerations relate to corrosive nature of the gas. This makes the application a pretty challenging one for any machine. Caterpillar provides guideline on gas quality and lists of substances and properties which must be maintained to ensure safe operation. This also helps plant operator to select the necessary treatment for the biogas. 

Our gas gensets are dedicated for biogas to get best performance but also to withstand the rigors of the application. This includes 
 • Specific engine compression ratio for higher efficiency, or adjustment due to site specific conditions to reduce power derate 
 • Selection of stainless steel aftercooler for improved protection against corrosion 
 • Adjustment of cooling temperatures to avoid condensation on key components or optimize thermal recovery
 • Specific layout and heat recovery equipment to optimize operation on biogas and components life
Beyond genset and power plant design, Caterpillar and our dealer network has developed services to support biogas operators through the life of the projects by providing specific maintenance plan for the equipment based on site conditions.  Another great service is Cat Connect remote asset monitoring.  You did a couple podcasts on this topic,  and by connecting the equipment to ensure improved condition monitoring, preemptive maintenance and faster reaction to maximize uptime. 

Every biogas plant is unique and this is why it is key for a customer to get in touch with our dealers and Cat sales team to make the right choices from day 1 and ensure optimum performance and equipment longevity over time.

Lou: There you have it folks.  I'd like to thank Sven Buhler for sharing his expertise with us today.  For more information on the use  of Biogas please go to www.cat.com/biogas   where you'll find lots of great information testimonials / animation / resources
In the meantime, If you’d like to suggest other topics for the program or have some feedback to share,  please write us here at powerbytes@cat.com or visit Cat Electric Power on Facebook or LinkedIn.   Please remember to subscribe to our Podcast wherever  you listen to your favorite podcasts.  Till next time, thanks for listening to Power Bytes and have a great day!