Pellet flue gas circulation and waste heat utilization process and system thereof

A pellet flue gas circulation and waste heat utilization process, which is carried out with a pellet flue gas circulation and waste heat utilization system;

• wherein the pellet flue gas circulation and waste heat utilization system comprises a grate, a rotary kiln and an annular cooler;
• in a pellet feeding direction, the grate comprises a blast drying section, an extraction drying section, a first preheating section and a second preheating section in sequence, the annular cooler comprises a first annular cooling section, a second annular cooling section, a third annular cooling section and a fourth annular cooling section in sequence, and a head end of the rotary kiln is connected to the second preheating section of the grate, and a tail end of the rotary kiln is connected to the first annular cooling section of the annular cooler;
• an outlet of the first annular cooling section of the annular cooler is connected to an inlet of the rotary kiln through a duct, an outlet of the rotary kiln is connected to an inlet of the second preheating section of the grate through a duct, and an outlet of the second preheating section of the grate is connected to an inlet of the extraction drying section of the grate through a duct;
• an outlet of the second annular cooling section of the annular cooler is connected to an inlet of the first preheating section of the grate through a duct;
• an outlet of the third annular cooling section of the annular cooler is connected to inlets of the blast drying section and the extraction drying section of the grate through ducts, respectively;
• outlets of the extraction drying section and the first preheating section of the grate are connected to an inlet of the third annular cooling section of the annular cooler through ducts;
• an outlet of the blast drying section of the grate is connected to an inlet of the fourth annular cooling section of the annular cooler through a duct;
• an outlet of the fourth annular cooling section of the annular cooler is connected to inlets of the first annular cooling section and the second annular cooling section of the annular cooler through ducts, respectively;
• wherein the process comprises preforming continuous flue gas emission monitoring in the ducts between the blast drying section and the fourth annular cooling section, between the extraction drying section and the first preheating section and the third annular cooling section, and between the fourth annular cooling section and the first annular cooling section and the second annular cooling section;
• wherein a control valve is arranged in the ducts between the blast drying section and the fourth annular cooling section, between the extraction drying section and the first preheating section and the third annular cooling section, and between the fourth annular cooling section and the first annular cooling section and the second annular cooling section;
• wherein in the pellet flue gas circulation and waste heat utilization process, 50%-100% of the flue gas from the blast drying section is introduced into the fourth annular cooling section after dust removal;
• the flue gas introduced into the first annular cooling section and the flue gas introduced into the second annular cooling section from the fourth annular cooling section have a ratio of 0:1-1:0;
• wherein the flue gas from the blast drying section after dust removal has a temperature of 80-150° C.;
• the flue gas from the extraction drying section and the first preheating section after desulfurization and denitrification has a temperature of 100-200° C.;
• the flue gas introduced into the first annular cooling section and the second annular cooling section from the fourth annular cooling section has a temperature of 100-200° C.;
• the flue gas introduced into the blast drying section and the extraction drying section from the third annular cooling section has a temperature of 250-350° C.;
• wherein the flue gas from the blast drying section after dust removal has an oxygen content of 17-20%;
• the flue gas from the extraction drying section and the first preheating section after desulfurization and denitrification has an oxygen content of 12-18%;
• the flue gas introduced into the blast drying section and the extraction drying section from the third annular cooling section has an oxygen content of 17-20%;
• the flue gas introduced into the first annular cooling section and the second annular cooling section from the fourth annular cooling section has an oxygen content of 17-20%;
• wherein dust removal equipment is further arranged between the blast drying section and the fourth annular cooling section;
• wherein a desulfurization unit is further arranged in the duct from the extraction drying section and the first preheating section to the third annular cooling section;
• performing denitrification in the duct from the extraction drying section and the first preheating section to the third annular cooling section;
• performing SNCR at a top of the second preheating section or in an inlet duct of the second preheating section;
• and
• performing SCR between the extraction drying section and the third annular cooling section.