Methods and systems for reducing carbon dioxide emissions

This application claims the benefit of International Application Number PCT/US2006/014495, filed Apr. 18, 2006, which claims the benefit of U.S. Provisional Application No. 60/672,279, filed Apr. 18, 2005, each of which is incorporated by reference as if disclosed herein in its entirety.

Climate change concerns have increased concerns over the level of carbon dioxide emissions from various processes. For example, the lime and cement industries are responsible for approximately 5% of global carbon dioxide emissions. Of these emissions, about 50% arise from the chemical liberation of carbon dioxide bound in carbonates and 40% from fuel consumption with the remainder associated with electricity use and transportation.

Lime is manufactured from limestone and dolomite by heating these materials in a limekiln. This process results in the evolution of carbon dioxide. The predominant reaction in limekilns, which is commonly referred to as the calcination reaction, is shown in the following equation [1]:

CaCO₃(s)→Ca(s)+CO₂(g)   [1]

Combustion of carbonaceous fuel is another process that generates carbon dioxide emissions. Currently, in one method used to reduce carbon dioxide emissions, lime is utilized to convert the carbon dioxide into limestone as shown in the following equation [2]:

CaO(s)+CO₂(g)→CaCO₃(s)   [2]

Then, the limestone is fired and converted back into lime as shown Equation [1] and this cycle repeats. However, after repeated cycling, sintering of the lime occurs and its capacity to capture carbon dioxide is greatly reduced.

A reduced emission kiln is disclosed. In some embodiments, the reduced emission kiln includes the following: a combustion zone for generating a heat energy, the combustion zone including an oxygen inlet and a fuel inlet; and a calcination zone for converting limestone into lime and carbon dioxide in response to the heat energy from the combustion zone, the calcination zone including an inlet for limestone, a conduit for directing the carbon dioxide to the combustion zone for use as a flood gas to control the heat energy, an outlet for directing the lime to a hydration chamber, and a carbon dioxide permeable membrane for separating the carbon dioxide in the calcination zone from other materials in the calcination zone and preventing the other materials from entering the conduit for directing the carbon dioxide.

A method of reducing emissions from a kiln is disclosed. In some embodiments, the method includes the following: providing a carbonaceous fuel and oxygen; combusting the carbonaceous fuel and oxygen to form a gaseous mixture including carbon dioxide, the gaseous mixture providing a heat energy; providing limestone; mixing the gaseous mixture with the limestone thereby heating the limestone with the heat energy; converting the limestone to lime and carbon dioxide; separating carbon dioxide from the lime and from other materials in the gaseous mixture; and mixing at least a portion of the carbon dioxide separated from the lime and from other materials in the gaseous mixture with the carbonaceous fuel and oxygen while combusting the carbonaceous fuel and oxygen thereby controlling the heat energy.

A reduced emission combustion system is disclosed. In some embodiments, the reduced emission combustion system includes the following: a boiler including a combustion zone for combusting carbonaceous fuels to form a gaseous mixture, the gaseous mixture providing a heat energy; a particle separator for removing fly ash and other particulates from the gaseous mixture; a calcium-based heat exchanger configured to mix and heat steam and slaked lime to form lime and steam, configured to capture the exothermic heat of reaction when the lime reacts to form slaked lime, and configured to recycle the slaked lime to the beginning of the calcium-based heat exchange system, the calcium-based heat exchange system including means for collecting dissolved slaked lime; a dry or wet scrubber for removing contaminants present in the gaseous mixture, the dry or wet scrubber including means for utilizing the dissolved slaked lime from the calcium-based heat exchange system; a carbon dioxide removal chamber for removing carbon dioxide present in the gaseous mixture, the carbon dioxide removal chamber including a mechanism for bringing the gaseous mixture into contact with lime or slaked lime to generate limestone; and a sorbent regenerator for generating lime and carbon dioxide from the limestone generated in the carbon dioxide removal chamber, the sorbent regenerator including means for providing the lime generated to the carbon dioxide removal chamber.