Electric Modular-Trigger Kiln with an Energy Recuperation System for Firing Vermiculte Concentrates

Abstract

Possibilities are considered for improving the energy efficiency of electric modular-trigger kilns for firing vermiculite concentrates. Rationale is given for introduction into the kiln construction of an additional "zero" module using secondary energy resources. A model of vermiculate thermal assimilation is provided, which takes account of thermal exergy accumulated within it, absorbed on heating, and transferred in a "zero" module into energy of grain mechanical transformation. In order to reduce loss of this exergy by vermiculite an original construction is proposed for a "zero" module, and prediction of the energy efficiency these kilns is provided.There are already more than ten years of experience of firing vermiculite in electric modular-trigger kilns. Each stage of their development makes a new contribution to improving the efficiency of these units and a reduction in firing specific energy consumption.During improvement, as with other complex systems, there are often new scientific and associated engineering solutions making it possible to raise them to the next level. In [1] an energy saving system was proposed and considered, including a recuperator for convective heat and radiant energy (secondary energy resources) and an additional "zero" heat-insulated, but not electrified, module using secondary energy resources (SER) for firing vermiculite within this module in a stage of partly incomplete heat assimilation.In this article on the basis of analyzing a new model, based on thermal latent exergy in vermiculite grains not considered previously (it is also considered as a SER), by accumulating and increasing its overall volume of heat assimilation energy, the possibility is demonstrated of its structural transfer into deep layers of grains and transformation into dehydration energy and vermiculite mechanical transformation.In order to minimize loss of exergy another structural solution of an additional module is proposed, thermally insulating vermiculite flow to a maximum.The aim of these studies was the possibility of improving the energy efficiency of electric modular-trigger kilns and substantiation of introducing into the kiln structure a "zero" module using SER, and also analysis of a model of vermiculite heat assimilation taking account of thermal exergy accumulated within it, transferred into mechanical transformation energy of its grains in the "zero" module.The term "exergy" signifies high quality energy, and its capacity for completing useful work under conditions of absence of equilibrium with the surroundings, i.e., that part of it that may be transformed and used. The specific case in question is singular. Here heat accumulated within vermiculite directly due to conduction is transformed into dehydration energy, phase transition, heating of water vapor and absorbed gases, and leads to completion of mechanical work in deep vermiculite layers [2].It has been shown in [3] that about 45% of thermal energy assimilated by vermiculite remains in material expanded and heated to 725 -750°C (q d ). ...

Energy Efficiency of the Electric Kilns With Movable Floor for the Various Size Groups Vermiculite Concentrate's Burning

“…Этот же объем V, м 3 , может быть выражен как суммарный объем тех же зерен по их условным диаметрам с учетом коэффициента пористости массива k, равного для вспученного вермикулита ~ 0,365 [10]:…”

“…где m -масса вермикулитового концентрата, находящегося на трех подовых плитах, кг. Так как масса дегидратирующего вермикулита снижается из-за выхода химически связанной и межслоевой воды на 20-24 % [10], в левую часть уравнения (7) следует ввести поправочный коэффициент 0,78. Тогда 0,78m -это масса движущегося однослойного потока в пересчете на вспученный материал, и она может быть определена через суммарный объем зерен, одновременно находящихся на трех подах печи по формуле (1).…”

“…Уравнение (7) с учетом равенства (4) можно привести к виду (10) а из него получить температурно-временную зависимость, определяющую режим работы печи с вибрационной подовой платформой (11) Удельная энергия теплоусвоения θ Σ для Кокшаровского вермикулита 921,8 кДж/кг установлена в последних экспериментах на физической модели и показана в работах [1,7].…”