Project Vision

Colorado’s Denver Zoo is evaluating a technology called biomass gasification to provide electricity and low temperature heat for the facility. This technology, which gasifies mixed wastes such as cardboard, wood, paper, and animal wastes, has both environmental and economic benefits. Implementing biomass gasification would reduce the zoo’s greenhouse gas (GHG) emissions, eliminate 750 tons of landfill waste per year, cut down on the amount of fossil fuel-produced electricity the zoo purchases each year, and decrease the consumption of natural gas for space heating. 

While gasification for mixed waste streams is not a new process, it’s important to note that the Denver Zoo project is truly innovative not just because of the scale of the facility and the diversity of the waste stream, but also because it will be implemented without impeding the zoo’s day-to-day operations. In the long term, this project will increase public awareness of renewable energy technologies, spotlight the con version of waste streams to useful energy (at a location that is visited by more than 2 million guests each year), and greatly enhance the zoo’s ongoing environmental education program.

The value of installing and operating a waste-to-energy gasification system at the Denver Zoo will help offset current energy costs and reduce the environmental impact of transporting waste to landfills. Currently the zoo spends close to $80,000 per year hauling away waste. Additionally, they work with a local composter to remove the portion of the waste stream that can be composted. When the gasification system is in place and operational, more than 1.5 million pounds of waste will be diverted from landfills every year. In addition, the zoo plans to add one to two qualified employees to its staff  to adequately oversee and operate the gasification system.

Selecting a Vendor

To get started on this effort, the Denver Zoo collaborated with Horizon Technologies to develop a vendor list of biomass gasifier companies, along with a set of evaluation criteria for selection. In response to a request the zoo made though the Technical Assistance Program, NREL staff assisted in reviewing credentials, and produced an independent evaluation of all qualified companies. Through a series of meetings and teleconferences, the selection team identified a set of potential vendors for further consideration. NREL helped develop a vendor questionnaire, and evaluate the vendor responses, although a final vendor has not yet been selected.

The greatest challenges for the zoo have been identifying and locating a gasifier that can handle the waste material at a price point that meets allowable budget constraints. In addition, the vendor needs to have sufficient commercial experience to provide process guarantees that the Denver Zoo needs in order to move forward.

During the vendor evaluation, the Denver Zoo has set important criteria to assure it selects the most appropriate and skilled organization for the job. The vendor must be able to handle a diverse waste stream and throughput capacity, while allowing the zoo continuous operation. It is also necessary that the vendor have experience with installing and placing the appropriate equipment. While the Denver Zoo has reviewed a range of vendors across the globe, they are focusing on vendors located and operating in the United States.

Project Finance

A project of this size requires significant funds to develop and finance. The Denver Zoo waste-to-energy project is part of the Asian Tropics exhibit, which is a $50 million effort. To date, Denver city and county bonds are funding $25 million of the overall cost. Additional funds have been contributed through private donations from individuals, foundations, and grants. The zoo is engaged in raising the final $6.5 million it requires for the project, and is searching for grants to fund the estimated $3.2 million cost for the gasification system.

Overcoming Barriers and Leading by Example

There are many considerations that come into play when choosing the kind of gasifier that can handle the Zoo’s waste. While there are several gasifiers that can theoretically accommodate a diverse waste stream, these specific gasifiers do not have an operational and performance track record to gauge their effectiveness. The most significant problem is turning the waste into a consistent feedstock, or fuel. The Denver Zoo has spent the last three years developing a process that they believe uniquely solves this problem. Several pieces of equipment will turn the waste into fuel and then convert that fuel into useable energy on site. Many of these pieces of equipment are based on custom designs and will become the intellectual property of the zoo.

The Denver Zoo is leading by example by implementing this unique gasification project. If successful, other zoos and many other operations around the world will be able to replicate similar projects and reap important economic and environmental benefits.

Please share any comments on projects unique to your communities that have benefited from technical assistance provided by the network of TAP representatives.

Content for this Blog post courtesy of George Pond, Denver Zoo, with Vickie Healey and Rich Bain, National Renewable Energy Laboratory