Because of the majority of China's pulping raw materials are non-wood fiber one (approximately over 50%), the majority of governances on black liquor in paper mills use alkali and acid recovery method. However, due to poor filtration performance of grasses pulp , more mixed cells, high viscosity and  large silicon content in black liquor and other characteristics, so that actual running effects of alkali recovery method are poor, the average alkali recovery rate is only about 60%, and the thermal efficiency is low, high operation cost, great difficulties on management . Therefore, it is difficult to completely solve the pollution problems about black liquor from straw pulp plants. Based on research and development in spray drying , evaporation and concentration for years,  combined with designing and operating experiences of single system about liquor evaporation, which are introduced abroad by our country. our company has  proposed and realized the processing flow on zero polluting discharge for black liquor governance(Figure 1).

Seen from the flowchart, coming out from the evaporator is only condensed water and thick black liquor, but the condensed water can be used as washing water for reuse, and then the thick black liquor proceeds into spray drying process. In exhaust gas from the drying system，  the dust content is less than 100 ~ 150 mg/ m³ in spray drying process, which can reach the national emission standard, without discharge of waste , at the same time  obtaining the lignin product. From the whole process of black liquor disposal, it is not difficult to find that there is no waste gas and waste emissions in the whole process, thereby realizing zero polluting emissions on black liquor governance. Papermaking black liquor is made as lignin products for comprehensive utilization, The extensive use of concrete water reducer, dispersant of coal water slurry, asphalt emulsifier, ceramics, oil exploitation additives etc., which is a development way to eliminate the destructions in ecological environment, create a friendly environment, natural harmony, truly to realize the unification of economic benefit, environmental benefit and social benefit.

Basic parameters of the spray drying equipment:

1、   Materials: black liquor, red liquor

2、   Inlet temperature: 280℃~430℃

3.  Outlet temperature: 110℃

4、   Dried powder production: 1000 kg/h ~4000kg/h

5、  Solid content: 40%~50%

6、   Heating source: direct coal hot air furnace with settling chamber, superheated steam, etc. (To be changed according to customers)

7、 Way of atomizing: High Speed centrifugal atomizer

8、   Heating method: direct coal hot air furnace is adopted (with four-level settling chamber, to effectively prevent the spark)

9、 Material recovery: first class of cyclone removing dust, second class of wet washing removing dust, recovery rate of 99.8%, in line with national emission standard.

10、Receiving: centralized receiving is adopted. At the bottom of the tower body, after powders are discharged out from the cyclone dust collector, all are sent by air conveying system into               the material bin in packaging workshop for packing.