Latest Low-NO x Combustion Technology for Pulverized-coal-fired Boilers
Kenichi Ochi Kenji Kiyama Hidehisa Yoshizako, Dr. Eng. Hirofumi Okazaki Masayuki Taniguchi, Dr. Eng. OVERVIEW: Hitachi has long been working on the development of low NOx combustion technologies to satisfy the worldwide need for environmental conservation and has devised the world-first concept of “inflame NOx reduction” which has been applied in the field of pulverized coal combustion technology in the HT-NR burner series. Hitachi has developed new technology to lower NOx levels even further by improving the structural design and operation of a two-stage air port system which is used in combination with in-flame NOx reduction. This work has been progressed using a large-scale combustion test facility that simulates actual furnace conditions and through the use of a numerical analysis technique developed in-house. The new technology can lower boiler outlet NOx by 40% for the same level of CO.
A reduced NOx reaction model for pulverized coal combustion under fuel-rich conditions
Abstract A reduced NO x reaction model was developed for analysis of industrial pulverized coal firing boilers. The model was developed from experiments of laminar premixed combustion under a variety of stoichiometric ratios, burning temperatures, coal ranks (from sub-bituminous coal to anthracite) and particle diameters. Calculations agreed with experimental results for NO x and nitrogen species (NH 3 and HCN), if the model assumed that the hydrocarbon radicals were formed not only from pyrolysis of volatile matter, but also from char oxidation and gasification. The presence of hydrogen in char at the final burnout stage supported this assumption. NO x reduction by hydrocarbon radicals was the most important reaction in high temperature (>1500 K), fuel-rich, char combustion regions. NO x reduction from nitrogen species was sensitive to peak NO x concentration in volatile combustion regions, but NO x emission downstream had little influence from the peak NO x concentration. The heterogeneous reaction between char and NO x was important for fuel-lean or low-temperature conditions.
Prevention of Barite Sag in Oil-Based Drilling Fluids Using a Mixture of Barite and Ilmenite as Weighting Material
Drilling high-pressure high-temperature (HPHT) wells requires a special fluid formulation that is capable of controlling the high pressure and is stable under the high downhole temperature. Barite-weighted fluids are common for such purpose because of the good properties of barite, its low cost, and its availability. However, solids settlement is a major problem encountered with this type of fluids, especially at elevated downhole temperatures. This phenomenon is known as barite sag, and it is encountered in vertical and directional wells under static or dynamic conditions leading to serious well control issues. This study aims to evaluate the use of barite-ilmenite mixture as a weighting agent to prevent solids sag in oil-based muds at elevated temperatures. Sag test was conducted under static conditions (vertical and inclined) at 350 °F and under dynamic conditions at 120 °F to determine the optimum ilmenite concentration. Afterward, a complete evaluation of the drilling fluid was performed by monitoring density, electrical stability, rheological and viscoelastic properties, and filtration performance to study the impact of adding ilmenite on drilling fluid performance. The results of this study showed that adding ilmenite reduces sag tendency, and only 40 wt.% ilmenite (from the total weighting material) was adequate to eliminate barite sag under both static and dynamic conditions with a sag factor of around 0.51. Adding ilmenite enhanced the rheological and viscoelastic properties and the suspension of solid particles in the drilling fluid, which confirmed sag test results. Adding ilmenite slightly increased the density of the drilling fluid, with a slight decrease in the electrical stability within the acceptable range of field applications. Moreover, a minor improvement in the filtration performance of the drilling fluid and filter cake sealing properties was observed with the combined weighting agent. The findings of this study provide a practical solution to the barite sag issue in oil-based fluids using a combination of barite and ilmenite powder as a weighting agent to drill HPHT oil and gas wells safely and efficiently with such type of fluids.