高碱煤碱金属迁移特性及其对受热面沾污行为的影响

The Alkali Elements Transition Characteristics and Their Effect on Ash Deposition Behaviour of High Alkali Coal

对新疆某台燃用新疆某高碱煤锅炉炉内灰中主要元素及矿物质迁移转化规律进行了实验研究与分析测试。研究结果表明:煤中20%的Na2O和10%的SO3由锅炉底渣排出,而其余部分的Na2O和SO3则随炉内烟气以气态或固态形式进入锅炉受热面,并在末级过热器、末级再热器受热面上主要以Na_2SO_4、CaSO4以及Na-Al-Si等低温硅铝酸盐的形式存在,从而引发锅炉高温受热面发生严重沾污、结渣等问题;通过对锅炉受热面沾污层断面的SEM-EDX分析表明:Na、Fe、Ca、S等元素是引起煤灰初始沾污的主要元素;在致密的初始沾污层上由Na_2SO_4、CaSO4等组成的大量沾污层,约有50%~96.14%的Na和Ca在600℃~850℃温度区间被硫化,且由于Na+的活性高于Ca2+,相同温度下Na的硫化比例要比Ca的硫化比例要高,除非在温度较高的区域(>1 429℃),由于Na的蒸发作用,导致Ca的硫化比例比Na的硫化比例要高。

The main ash elements as well as mineral transition characteristics in a real boiler with using Xinjiang high alkali coal was studied in this paper.The test results were showed that around 20% of Na2 O and 10% SO3 in raw coal ash were drained out from the bottom of boiler,the other Na2 O and SO3 were flew into the flue gas as gas or solid phase,some of them will be deposited on the surface of final heater and reheater tubes.The elements of Na and S in the deposit were mainly existed as Na_2SO_4,CaSO4 and some Na-Al-Si salts and that is the main reason for serious ash fouling problems on final heater and reheater.The initial ash deposition layer were mainly composed by Na_2SO_4 and CaSO4.Around 50% ~96.14% of Na and Ca were sulfureted in the temperature range from 600℃to 850℃,and in this temperature range the percentage of sulfureted Na is higher than that of sulfureted Ca due to the higher reactivity of Na＋,while at high temperature,above 1429℃the percentage of sulfureted Na is lower than that of sulfureted Ca due to vaporization of Na.