Energy saving in ceramic tile kilns: Cooling gas heat recovery

Abstract

A great quantity of thermal energy is consumed in ceramic tile manufacture, mainly in the firing stage. The most widely used facilities are roller kilns, fuelled by natural gas, in which more than 50% of the energy input is lost through the flue gas and cooling gas exhaust stacks. This paper presents a calculation methodology, based on certain kiln operating parameters, for quantifying the energy saving obtained in the kiln when part of the cooling gases are recovered in the firing chamber and are not exhausted into the atmosphere. Energy savings up to 17 % have been estimated in the studied case.Comparison of the theoretical results with the experimental data confirmed the validity of the proposed methodology. The study also evidenced the need to improve combustion process control, owing to the importance of the combustion process in kiln safety and energy efficiency. KEYWORDS: ceramic tile, roller kiln, heat recovery, energy efficiency HIGHLIGHTS:Some energy input (30 -35%) in ceramic roller kilns is lost through the cooling gas stack.Cooling air is directly recovered in the combustion chamber, providing oxygen. This energy recovery from the cooling gas stack has been quantified.It has been proven that the proposed methodology to estimate energy savings is valid.

A review on waste heat recovery from exhaust in the ceramics industry

“…The application is limited due to the production of acidic combustion gases and other implications such as foaming. Some applications use a thermal oil as a working fluid to transfer the recovered heat to the drying and firing stages [10,13]. Fig.…”

CFD analysis of a full-scale ceramic kiln module under actual operating conditions

“…In [2] a theoretical formulation for the prediction of the kiln operating characteristics has been proposed under regime conditions and many simplifications to the physical phenomena had to be made in order to close the mathematical model. Similar approach is adopted also in [3] in which the main focus was the assessment of the heat transfer between the hot air flow and the kiln walls. The numerical simulation becomes a valuable tool in investigating the performance of complex physical systems including different physical phenomena.…”

Simulación de la transferencia de energía en hornos monoestrato de rodillos para la cocción de baldosas cerámicas

“…La estimación del caudal de aire de enfriamiento incorporado al calentamiento se realizó mediante el método descrito en la referencia [16]. En este método, partiendo de los caudales de combustible y comburente determinados experimentalmente, se plantean los balances de materia descritos en §3.3.2.1, de manera que la fracción volumétrica de O 2 en los humos en cualquier posición a lo largo del horno puede expresarse como una función del caudal de aire de enfriamiento.…”

“…Para alcanzar estas temperaturas, se dispone de un sistema de dilución que introduce aire ambiente en la corriente de humos, justo aguas arriba del ventilador. Este aire de dilución, junto con el aire parásito que accede por la boca del horno, puede llegar a constituir más de 2 3 del caudal de gases en la chimenea de humos [16], de donde se deduce que la temperatura de los humos en la entrada del horno es de al menos 300 o 400°C.…”

“…Esta energía se corresponde con la modificación en la entalpía de las baldosas al pasar de crudas a cocidas. Puesto que se trata de una modesta fracción del calor total aportado, suele argumentarse que la operación de cocción es extremadamente ineficiente [13,16,22], aunque quizás este razonamiento sea un tanto simplista [23].…”