New Process for Achieving Very Low Nox

Over the last two and a half years, Covanta Energy, working with their technology partner, Martin GmbH of Germany, has developed and commercialized a new technology for reducing NOx emissions from Energy from Waste (EfW) facilities. NOx levels below 60 ppm (7% O2) have been reliably achieved, which is a reduction of 70% below the current EPA standard and typical levels of today’s EfW facilities in the United States. This technology represents a significant step forward in NOx control for the EfW industry. The technology, known as VLNTM, employs a unique combustion system design, which in addition to the conventional primary and secondary air streams, also features a new internal stream of “VLNTM-gas,” which is drawn from the combustor and re-injected into the furnace. The gas flow distribution between the primary and secondary air, as well as the VLNTM-gas, is controlled to yield the optimal flue gas composition and furnace temperature profile to minimize NOx formation and optimize combustion. The VLNTM process is combined with conventional, aqueous ammonia SNCR technology to achieve the superior NOx performance. The SNCR control system is also integrated with the VLNTM combustion controls to maximize NOx reduction and minimize ammonia slip. A simplified version of the process, known as LNTM, was also developed and demonstrated for retrofit applications. In the LNTM process, air is used instead of the internal VLNTM gas. The total air flow requirement is higher than in the VLNTM process, but unchanged compared to conventional systems, minimizing the impact on the existing boiler performance and making it ideal for retrofit applications. Covanta first demonstrated the new VLNTM and LNTM processes at their Bristol, Connecticut facility. One of Bristol’s 325 TPD units was retrofitted in April of 2006 to enable commercial scale testing of both the VLNTM and LNTM processes. Since installing and starting up the new system, Bristol has operated in both VLNTM and LNTM modes for extended periods, totaling more than one year of operation at NOx levels at or below 60 ppm (7% O2). The system is still in place today and being evaluated for permanent operation. Based on the success of the Bristol program, Covanta installed LNTM NOx control systems in a number of other existing units in 2007 and 2008 (total MSW capacity of over 5000 TPD), and is planning more installations in 2009. All of these retrofits utilize the Covanta LNTM system to minimize any impacts on existing boiler performance by maintaining existing excess air levels. Going forward, Covanta is making the LNTM technology available to its existing client base and is working with interested facilities to complete the necessary engineering and design modifications for retrofit of this innovative technology. For new grassroots facilities, Covanta is offering the VLNTM system with SNCR as its standard design for NOx control. An additional feature, particular to VLNTM, is the reduced total combustion air requirement, which results in improved boiler efficiency. This translates into increased energy recovery per ton of waste processed. In addition to introducing the VLNTM and LNTM processes, this paper will provide an overview of the Bristol development and demonstration project. NOx and NH3 slip data from Bristol will be presented, illustrating the extended operating experience that has been established on the system. Other operating advantages Proceedings of the 17th Annual North American Waste-to-Energy Conference NAWTEC17 May 18-20, 2009, Chantilly, Virginia, USA