STATUS OF NOx EMISSIONS FROM COAL FIRED UTILITIES
Dr. Koturs Narsimhan
(former director of Central Fuel research Institute, Dhanbad, India)
March 14, 1997 at 3:00 pm
Ben Bandy Conference Center
Center for Applied Energy Research
A study is made on the emissions of oxides of nitrogen (NOx) from power plants in the country in order to:
- (i) Assess the impact of coal based units on the environment
- (ii) Gauge the utility of NOx reduction technologies that are currently in vogue.
86 percent of 5.5 million tons of NOx emitted during the year 1999 came from exclusively coal-based units. Such emissions ranged from 0.12 lbs/mmBtu to 1.8 lbs/mmBtu in sharp contrast to oil and gas fired units that had a shorter range. 419 coal-based units equipped with NOx control measures emitted 2.14 million tons (0.4 lbs/mmBtu on average) compared to 2.64 million tons (0.58 lbs/mmBtu on average) from 634 units that had no control.
Most of the coal-based units having controls acquired them during the years 1995-1999. A comparison of NOx emissions from them before and after the retrofit has brought out some interesting observations. The extent of reduction achieved with the same technology in similar units has varied considerably. Not only in many of the installations has the reduction fallen short of expectations but also in several of them the result is even negative. A significant number of coal-fired units without any control had NOx levels equal to or lower than the median values of similar units with controls imposed. The impact of the operating technologies can therefore, be only considered as unit specific. These anomalies might have arisen due to incompatibility of the system design to the fuel characteristics - both physics and chemistry.
Eventually it may be necessary to reduce NOx to below 0.1 lbs/mmBtu. For this purpose a combination of technologies may be required involving Selective Catalytic Reduction (SCR), Coal Reburn (CR) and some others unique to each case. A better understanding of the relation between system design and fuel characteristics could minimize the number of technologies needed.