Sub-micron particle number emission from residential heating systems: A comparison between conventional and condensing boilers fueled by natural gas and liquid petroleum gas, and pellet stoves

Pollutant emissions from residential heating systems represent a main concern in terms of outdoor air quality. Differently from other pollutants, sub-micron particle emission from heating systems has not yet been exhaustively characterized by the scientific literature, with limited data available, in particular, for gas-fueled boilers. In the present paper, an experimental campaign to measure the sub-micron particle number concentrations and distributions at the stack of different automatically-fed small-scale heating systems (conventional and condensing boilers fueled by natural gas and liquid petroleum gas, and pellet stoves) was performed. Based on the measured concentrations, corresponding emission rates and emission factors were also estimated. The results of the experimental campaign revealed that the highest concentrations were measured for pellet stoves (median value >10⁷ part. m^-3), whereas conventional (about 1 × 10⁶ part. m^-3) and condensing boilers (<10⁶ part. m^-3) presented much lower concentrations. No effect of the fuel (natural gas, liquid petroleum gas) on the total concentration measured at the stack of boilers was recognized, whereas a smaller distribution mode (at 10 nm) was measured for gas-fired boilers. Because of the particle concentration values, the highest particle emission rates and factors were the pellet stove ones (median values of 2.1 × 10¹⁵ part. h^-1 and 8.4 × 10¹³ part. kWh^-1, respectively), whereas emission rates for conventional and condensing boilers were about 5 × 10¹³ part. h^-1 and 2 × 10¹³ part. h^-1, respectively. The estimated emission factors were also adopted to perform a simplified evaluation of the relative contributions of the investigated automatically-fed small-scale heating systems in terms of particle number on a national scale (Italy): we obtained that the pellet stove contribution is the main one as it accounts for 87% of total emissions of particle number for heating purpose.

Municipal reclaimed water for multi-purpose applications in the power sector: A review

Wastewater and power utilities in the United States have an enormous opportunity to collaborate on the mutually beneficial uses of reclaimed water. Despite close proximity to wastewater facilities, only a limited number of power plants are currently using municipal reclaimed water for cooling tower and boiler applications. Through a review of the literature, this document aims at creating a more perspicuous understanding of the reuse of reclaimed water for power plant applications, particularly as pertains to those associated with cooling towers and boilers, by highlighting the drivers of current implementation, regulatory issues and treatment goals, and available treatment technologies. Through an in-depth analysis of case studies, the review also highlights key examples of reclaimed water reuse projects at power utilities together with the related benefits and challenges.

Process aspects in combustion and gasification Waste-to-Energy (WtE) units

The utilisation of energy in waste, Waste to Energy (WtE), has become increasingly important. Waste is a wide concept, and to focus, the feedstock dealt with here is mostly municipal solid waste. It is found that combustion in grate-fired furnaces is by far the most common mode of fuel conversion compared to fluidized beds and rotary furnaces. Combinations of pyrolysis in rotary furnace or gasification in fluidized or fixed bed with high-temperature combustion are applied particularly in Japan in systems whose purpose is to melt ashes and destroy dioxins. Recently, also in Japan more emphasis is put on WtE. In countries with high heat demand, WtE in the form of heat and power can be quite efficient even in simple grate-fired systems, whereas in warm regions only electricity is generated, and for this product the efficiency of boilers (the steam data) is limited by corrosion from the flue gas. However, combination of cleaned gas from gasification with combustion provides a means to enhance the efficiency of electricity production considerably. Finally, the impact of sorting on the properties of the waste to be fed to boilers or gasifiers is discussed. The description intends to be general, but examples are mostly taken from Europe.