Low Stoichiometric Ratio Research Articles

石炭流動層燃焼装置内における同時脱硫脱硝特性

A fluidized bed combustor of coal can be considered as a multifunctional process which performs functions of in situ controls of sulphur dioxide and nitric oxide emissions as well as a function of combustion. However the symbiotic realization of these functions in a compact chamber has proved a difficult task so far, since the design parameters influencing the emission control of pollutant and the combustion efficiency do involve complicated interactions.In the present study, the coal combustion with in situ sulphur retention was conducted using an experimental fluidized bed under the conditions of single and two stage combustion, and the performances of the three functions were measured under the relatively wide range of stoichiometric ratio of primary air choosing Ca/S ratio as a parameter. Furthermore, the effects of the injection height of secondary air on the performances were tested and the concentration profiles of SO2, H2S, NO and NH3 in the freeboard were measured under the condition of staged air firing. The most important result obtained was that the increased retention of sulphur dioxide as well as the reduced emission of nitric oxide was observed with the increased height of secondary air injection at the relatively low stoichiometric ratio of primary air. Thus the possibility of the symbiotic realization of simultaneous emission controls of sulphur dioxide and nitric oxide was experimentally demonstrated.

Problems associated with stannous 99 mTc- radiopharmaceuticals

Possible reasons for anomalous in vivo behavior of 99 m Tc radiopharmaceuticals are evaluated. The complicated and poorly understood solution chemistry of technetium as well as tin (II), the most widely used reducing agent, is shown to contribute to problems. Unreliable performance of stannous kits is deduced to be partly due to initial oxidation and hydrolysis of tin (II) as a result of poor formulation, and also due to low stoichiometric ratios of complexing agent to tin. The kits could fail in two ways: (1) only a fraction of the original tin may be available in the desired form at reconstitution; (2) undesirable side reactions of tin and technetium may occur. Evaluation of generator as well as instant technetium has occasionally revealed situations where the carrier content of 99 m Tc solutions could exceed the reductive capability of the stannous ion; this becomes critical with kits containing a very small quantity of Sn (II) in the “usable” form. Parameters for effective performance of tin (II) containing kits are examined, and a titration method allowing for in vitro evaluation of available kits is presented. A model procedure for preparing stable Sn (II) kits has been developed.