Research On The Releasing Regularity Of Chlorine In Straw During Pyrolysis Process

Because of the high chlorine content, thermal conversion processes of rice straw will encounter many problems, such as corrosion of metals at high temperature, pollution in the heating surface, slag aggregation in the furnace and so on. Thus, the regularity of chlorine releasing during pyrolysis from 300℃to 900℃was discussed based on the results of experiment and Factsage software. Moreover, the precipitation mechanism of chlorine releasing during pyrolysis was analyzed.When straw was pyrolysed below 600℃, the chlorine releasing rate increased with pyrolysis temperatures ranging from 300℃to 600℃, but the increasing trend became gentle. About 30% of chlorine was released at 600℃in the following two ways:one way is that the chlorine in KCl reacts with hydrated proton produced in pyrolysis and then is released in the form of HC1, and another way is that organic chlorine in straw is released by chemical reaction. The chlorine in semi-char has two existence forms. Most exists by ionic bond, the removal of which has almost nothing to do with thermal treatment methods. The remaining is in the semi-char by physical adsorption. When straw was pyrolysed from 600℃to 900℃, the chlorine releasing rate increased, and about 70% of the total chlorine was released at 900℃in half an hour. The chlorine contents of semi-char increased at first and then decreased with pyrolysis temperatures ranging from 300℃to 900℃, and the maximum value was at 600℃.The calculated results of Factsage software showed that the chlorine almost did not release below 600℃; HC1 was the major form of the releasing of little chlorine. Above 600℃, chlorine began to release in the form of gaseous KCl, (KCl) 2 and HCl, and with the raising of temperature, gaseous KCl gradually became the major form of chlorine releasing. At 850℃, there was no chlorine left in the semi-char. When increasing the pressure, it would inhibit the chlorine releasing rate, while increasing the moisture in the atmosphere, it would promote the precipitation of chlorine.