Making air, pollution free

Making air, pollution free

5:26 AM, 22nd August 2017
Shrish Patel, PhD Researcher at Orlov Materials Lab of Stony Brook University.

In an interview, Shrish Patel, PhD Researcher at Orlov Materials Lab of Stony Brook University with Chemical Today Magazine talks about the ways in which air pollutants can be minimized in the cement industry.

Removing air pollutants.

The current research is to understand the interaction of nitrogen dioxide and sulfur dioxide with crushed demolished concrete. These interactions facilitate adsorption and conversion of these oxides on the concrete surfaces. Such removal of air pollutants can be affected by several parameters, such as age, cement content, type of aggregate used, the source of demolished concrete, chemical composition, porosity. Relating these parameters to mechanisms of removal is an important part of our project.

Concrete interaction and elimination of sulphur and nitrogen oxides.

The calcium hydroxide in the concrete reacts with nitrogen dioxide to form calcium nitrate and calcium nitrite.

                  2Ca(OH)2 + 4(NO)→ Ca(NO3)2 + Ca(NO2)2 + 2H2O

Moreover, calcium nitrite will further decompose to calcium nitrate in the following manner

                  3Ca(NO2)2 + 2H2O→ Ca(NO3)2 + 4NO + 2Ca(OH)2

The possible reaction of calcium hydroxide and sulfur dioxide is

                  Ca(OH)2 + SO2 → CaSO3.½ H2O + ½ H2O

Use of waste concrete to minimize air pollution.

Currently, the main technique employed in cement industry to mitigate NOx emission is a selective catalytic reduction (SCR) and selective noncatalytic reduction (SNCR). SCR uses ammonia and a catalyst to selectively reduce NOX emissions from exhaust gases. A much more popular approach is SNCR, which applies ammonia injection technique in the flue-gas at an appropriate temperature. The efficiency of this process varies from 25 to 85 percent.

To minimize air pollution and its effect on climate change, there is a need to achieve much higher removal efficiency. Our proposed solution is an “add on” process to the existing cement manufacturing process, which will be a completely new approach in mitigating NOx and SOx emissions. Given a significant potential of waste concrete to achieve a substantial degree of NO2 or SO2 removal it can be injected in a similar manner, or used as an adsorbent bed in the downstream part of flue gas treatment.

Raw materials present in concrete that release sulfur dioxide.

The major raw materials used in cement industry are CaCO3, SiO2, Al2O3 and others. Portland cement is a fine powder that consists of a mixture of the tricalcium silicate (3CaO.SiO2), dicalcium silicate (2CaO.SiO2), tricalcium aluminate (3CaO.Al2O3) and tetracalcium aluminoferrite (4CaO, Al2O3.Fe2O3).

The SOx emission can take place from various sources, such as the sulphur containing raw material in the form of pyrite (FeS2)

                  2FeS2 + 11/2 O2 → Fe2O3 + 4SO2

From the burning of sulphur present in fuel used in the cement kiln

                  Fuel S + O2 → SO2

Kiln feed containing carbon might cause SO2 emissions

                  4CaSO4 + 2C → 4CaO + 2CO2 + 4SO2

Renewable materials used in concrete to reduce sulphur dioxide emissions.

Optimizing combustion condition and improving energy efficiency of concrete production can substantially reduce nitrogen dioxide emissions. In addition, utilization of low sulphur fuel can also reduce environmental impact. In addition, geopolymer cement and magnesium oxychloride cement (MOC) can be alternative to ordinary portland cement (OPC) can make a positive difference. Both the cement types are manufactured at lower temperature compared to that for portland cement, minimizing emissions.

Advantage of using this concept over other solutions.

The photocatalytic activity of TiO2 to mitigate nitrogen dioxide is one of the extensively studied methods. However, we believe that cement and concrete can be a cheap and effective alternative to use as an adsorbent for emission reduction. Recycling crushed demolished concrete as an absorber is way better than using an expensive catalyst.

Commercializing the research.

There are plans to work with concrete manufacturers and air pollution control industry to develop more commercially relevant solutions. This research directly benefits the construction sector. Indirectly, transportation sector can also benefit from the proposed approach, given positive benefits of air pollution reduction.

This research will be beneficial for adoption in emerging markets as well. Our proposed solution is an “add on” process step to the current techniques used in cement industry to control NOx emission. Our researched solution will help the industry reach complete removal of NOx emission.

Plans for future research.

Our future research focuses on the absorption of pollutants as a function of temperature, humidity, concentration, concrete composition and others. Moreover, we are also trying to identify which component or phases is more active towards NOx absorption.

Challenges faced while doing the research.

The challenging part of the research is to optimize the maximum uptake of SOx and NOx uptake and understand the mechanisms of interactions of these pollutants with a rather complex and heterogeneous material as concrete.

© Chemical Today News 

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