The cement industry today faces yet another challenge on emission norms. We explore some of the solutions which are being tried and those that have been tried in other parts of the world.
In the entire process of cement manufacture, pyro processing is the most critical process. It not only entails the conversion of heat into chemical energy but the efficiency of the process also decides the bottom line of a plant.
Pyro processing (from Greek +á-à-ü++-é = fire) is a reaction in which materials are subjected to high temperatures (typically over 800 °C) in order to bring about a chemical or physical change. It includes such terms as calcination, sintering or roasting etc.
In the current issue we are trying to focus on some of the technological advances on the backdrop of the changes which have been announced by the Ministry of Environment, Forests & Climate Change in the recent past regarding the emissions from cement plants. The changes announced are in the larger interest of protecting the environment and to align the regulations with that of the developed world. The moot question now is how the industry can technologically face the challenge. To know more on the specific changes in the emission norms and how they compare with those in the other countries, refer to the article by CH Persson of Yara Environmental Technologies AB, Sweden.
We have been successful in getting a viewpoint from Jayant Saha who is having extensive experience in the role of a consultant. He describes that most of the emissions are in the form of particulate matters, CO2, SOx, NOx and sometime toxic matters containing mercury, other heavy metals and persistent organic pollutants. Almost all chemical pollutants are generated in the pyro section. He has further gone into details on how NOx is formed (a chemical reaction of atmospheric nitrogen at a temperature greater than about 1,200 °C by direct oxidation). Since the flame temperature in a cement rotary kiln is about 2,000 °C, considerable amount of thermal NO is generated. Saha provides us the information on Primary NOx Reduction Measures and Secondary NOx Reduction Measures (SNCR).
We would draw the attention of our readers to the article from FLSmidth which describes the use of an advanced technique like Computational Fluid Dynamics (CFD) in studying the flow pattern of a burner. FLSmidth has a burner called Duoflex which can be used for different kinds of fuels. We would like to remind our readers that today coal is not the only fuel used in the kilns but there are alternate fuels, agri-wastes and industrial wastes which are being tried as fuel. The kiln should be capable of handling different kinds of fuels. The trials with the burner were not taken with coal as a fuel but with natural gas and peat as fuels. It is interesting to note that the company took help of the CFD technique to understand the performance of the burner. We would urge our readers to read the complete article submitted by Arun Appadurai of FLSmidth. To know more on CFD, please refer to the information given separately in the cover story. CFD in the real sense is an advanced technique which is being used presently to simulate the real conditions at the design stage itself. The success rate of any experimentation can be high if CFD technique is used before investing in CAPEX.
The article by CH Persson of Yara Environmental Technologies AB, Sweden is quite exhaustive and covers all aspects of the system used in NOx reduction and various options available like SCR (Selective Catalytic Reduction) and SNCR (Selective Non Catalytic Reduction). Incidentally Yara has a very successful track record of serving the cement industry across the globe. One can find a comparison between SCR and SNCR systems in the article. The interesting part of the comparison is that it covers both the operating and capital cost.
Under the heading Technoloy, we have covered a case study on installation of new kiln line by IKN in Turkey. While designing an inline calciner, a low NOx duct was installed to ensure an efficient mixing of meal and fuel with the oxygen-rich tertiary air. The lower part of the calciner had a width of 4.35 sq m and the upper part had a diameter of 4.1 sq m leading to a swirl head to ensure generation of CO, which reduces a good portion of nitrogen oxides. The calciner burner is designed to burn any combination of pet coke or coal.
It is important to note that the project has been completed with performance guarantee.
Though technically it´s feasible to comply with the revised emission norms which you can see from what is covered in cover present issue, the job is not going to be easy; more particularly for older plants. However, given the capability of the Indian cement industry, it can take on the challenge.
Box Exploring CFD
CFD is the use of applied mathematics, physics and computational software to visualise how a gas or liquid flows - as well as how the gas or liquid affects objects as it flows past. CFD is based on the Navier-Stokes equations. These equations describe how the velocity, pressure, temperature, and density of a moving fluid are related.
CFD has been around since the early 20th century and many people are familiar with it as a tool for analysing air flow around cars and aircraft. As the cooling infrastructure of server rooms has increased in complexity, CFD has also become a useful tool in the data centre for analysing thermal properties and modelling air flow. Simply by changing variables, the administrator can visualise how cold air will flow through the given vessel or container under a number of different circumstances. CFD in the cement industry is a computer aided solution technique used to describe and simulate flow-related physical phenomena (e.g. fluid flow, heat transfer and combustion). Various cement, lime and power plant applications that can be analysed using CFD include:
Pre-heaters, Pre-calciners, kilns, coolers and boilers.