As the air pressure is high, the horizontal air preheater should be adopted to avoid air leakage. Air is in the tube and flue gas is out of the tube. And it is of in-line arrangement, tube diameter is Ф40x1.5. To prevent wear and tear, the first row, the second row and the tubes on two sides which scour along with the flue gas should adopt the thick wall tube (Ф42x3). 
Tube box of preheater is divided into three sections. The upper one is for the secondary air preheater, the horizontal pitch is 68mm and the vertical pitch is 60mm. The lower two are for the primary air, the horizontal pitch is 65mm and the vertical pitch is 60mm. 
To avoid low-temperature corrosion, the lowest tube box adopt ND steel.