Improving the Operation of an Automatic Wood Chip Boiler by Optimizing CO Emissions

Abstract

In wood chip boilers, CO emissions can be reduced by improving the control over the combustion process. To minimize emissions and optimize efficiency, the excess air ratio, the primary and secondary air distribution systems, and the fuel feed rates must be adjusted to maintain stable combustion. An extensive series of wood combustion tests was performed in a grate automatic 180 kW th boiler. The level of influence exerted by wood parameters, such as the origin, particle size, and moisture content, and combustion parameters, such as the excess air ratio, air distribution, and boiler load, were studied. The most important characteristic of wood with regard to CO emissions is the moisture content. The combustion tests with both types of wood chips and sawdust show that the CO emissions and excess air ratio decline when the fuel power increases. The direct relationship between the excess air ratio and the level of power facilitates the optimization that minimizes the CO emissions. The control system must be based on a fluctuating O 2 concentration in the exhaust gas by varying the excess air ratio relative to the power demand. The excess air ratio needed to implement the optimal conditions should be between 2.0 and 2.5 at 100 kW th , between 1.9 and 2.1 at 135 kW th , and between 1.7 and 1.9 at nominal power.

Low-Quality Fuels for Small-Scale Combustion Boilers: An Experimental Study

“…These curves are quite similar to those obtained by other authors who studied different fuels in the same unit with a lambda control system. They are also similar to those obtained with other type of process controls applied to a medium-scale boiler model or even applied to a small biomass stove . In the case of the medium-scale boiler, a clear defined curve was also obtained at a partial load, which did not happen to be our case.…”

“…The quick test determines the optimal lambda (interval) for each fuel by analyzing the measured dependence of CO emissions and lambda. This strategy is similar to those proposed by Petrocelli et al 57 for pellet stoves or by Quintero-Marquez et al 58 for a 180 kW grate automatic boiler. If a fuel is tested in a wide range of air excess ratios, we observe a prompt decrease in the instantaneous CO emissions when lambda increases and the fuel begins to burn "properly".…”

A Comprehensive Technoeconomic and Environmental Evaluation of a Hybrid Renewable Energy System for a Smart Farm in South Korea

“…where the values of C, H, S, and O are the dry ash-free mass fractions of the biomass and can be obtained from the ultimate analysis in Table 3. It is considered that the air is introduced with an excess ratio of 1.8, which is within the applicable range of boilers [35,36], and it is calculated in a calculator block (AFR-BURN). Thus, the mass flow rate of the air, in accordance with the mass flow rate of the wood pellets, is estimated and applied to the air stream flow.…”