Webinar explores biogas considerations, challenges and financing

By Anna Simet | November 05, 2014

Caterpillar Inc. installed its first biogas systems in the early 1980s beginning with landfill sites, and since then, the company has seen business soar with installation of over 1.5 gigawatts of capacity worldwide—more than 1,500 units, according to Ben Mathews, Caterpillar Electric Power & Gas.

Today, Caterpillar offers units that range from 50 kilowatts to close to 4 MW and can provide bare gensets to complete combined-heat-and-power solutions, Mathews said.

Overcoming biogas project challenges and pitfalls was discussed at length during a recent Biomass Magazine webinar, during which Mathews discussed considerations for gensets, pros and cons of enclosures verses buildings and operations and maintenance considerations.

Hydrogen sulfide corrosion and siloxane deposits are potential contaminant issues a biogas developer might face, but there are strategies to deal with them, one of which is gas pretreatment, or cleaning the gas to natural gas quality. “It does cause a significant impact to your capital cost, and as you scale down in size, that impact is much larger, so that’s something to be aware of,” Mathews said.

However, pretreatment allows for more predictable maintenance intervals because consistent, high-quality gas, and high-efficiency engines that have less of a margin for contaminants can be utilized.

Other strategy contamination strategy is what Mathews called fortifying or “hardening” the engine. “This is something we see in North America a lot of times, because here, we’re competing against very aggressive utility prices and don’t have a large margin or gap for power purchase agreements….with a hardened engine you have a lower capital cost up front because you’re not investing as much, but you do see some increased maintenance intervals.”

Cat hardens an engine by replacing bright metals with stainless steels—anything that might come into contact with containments—elevate jacket water temperatures to prevent condensation, and optimization of valve design to deal with abrasive components.

On buildings verses enclosure tradeoffs, Mathews said that in general, a building is recommended wherever possible and wherever it makes sense financially. “It provides the optimum environment for service,” he said. “There is lots of room to work around engine and you’re not exposed to the environment, so if you’re working in northern Canada where it’s [climate] less than ideal, you’ll at least be sheltered.”

Buildings increase total uptime and availability, Mathews added, but closed solutions require lower CAPEX. “As a general rule of thumb, for two units or less, an enclosure makes sense—you have reduced engineering, procurement and construction costs, and then turn around from order to delivery and power production is quicker.

On operations and maintenance considerations, Mathews said gas engines should be loaded at 100 percent if possible. “That’s what they’re designed for,” he said. “As you go down in load, because the digester is still building up gas supply or it’s not producing the level of biogas anticipated, you’ll start to run into issues.”

A general rule of thumb is to size for greater than an 85 percent load, and most engine manufacturers have a minimum of 50 percent load. “Even if it’s usually at 50 percent, it needs to see 75 to 80 percent at some time to burn out the oil,” Mathews said.

Keeping overhead lifting capacity in mind is also a must. “For a G3520 engine, for example, cylinder heads are between 100 and 120 lbs. If you’re doing a top-end overhaul without lifting capacity, you have to increase labor, as well as time, to make that service happen.”

Not all operations can afford to have full-time operators due to the size of the project, but when possible, it makes a big difference, Mathews added. And a good predictive maintenance strategy can reduce costs by more than 15 percent. “What I mean by this is monitoring everything…valve recession, oil consumption, fuel consumption, exhaust emissions…by looking at different engine components, you can see how its wearing and how to do maintenance intervals—repair before failure. Lots of times if you repair after, you pick up some collateral damage.”

Mathews’ last points touched on the importance of availability, and how it often gets overlooked. “What I mean by that is revenue is lost every time the generating equipment does not operate—such as maintenance and repair, or when fuel supply is reduced or interrupted. We can control availability by minimizing downtime.”

Ways to do that maximize availability includes choosing technology providers that have demonstrated good durability with the type of gas you have at your site, or has a proven track record, and also making sure that the product is being applied properly. “If you have a higher-emission engine, make sure that you match it with a cleaner biogas—use the guidelines of the engine manufacturer.

Being aware of spare parts immediately available is advised, Mathews concluded. “What do you have on hand at the distributor dealership, what do you have in-country? It’s good to understand that in case something goes down—when you’ll have that part, and the same goes with service. Where are the service techs coming from? If there is an unplanned failure, that’s when availability is the most impacted—when can the tech be there?”

Other webinar speakers included Paul Owen of Cat Power Finance and Ross Buckenham of California Bioenergy LLC.

A free recording of the webinar will be available here