Flow control for polysilicon

Improving reliability and productivity of your process

Polysilicon is produced from metallurgical grade silicon by a chemical purification process. The demanding process includes high temperatures and abrasive materials, and therefore reliable valves of high quality are needed. Valmet has polysilicon application experience and our Neles™ valves have proven performance history and are designed for efficient and reliable process operation.



High performance

Polysilicon process overview

A typical polysilicon proces is using SiO2 (quartz sand) as raw material to produce metallurgical grade Si, also known as MG-Si. MG-Si is obtained in an arc furnace with existence of carbon.

MG-Si is purified through the following processes:

First, Si is converted to SiHCl3 (trichlorsilane, also known as TCS) via below reaction:

Si  +  3HCl  →  SiHCl3  +  H2

The reaction takes place at around 300 °C in a fluid bed reactor with forming possible byproduct such as SiCl4 and SiH2Cl2. Secondly, the SiHCl3 is distilled, resulting in extremely pure SiHCl3. 

Finally, a chemical reaction takes place in a chemical vapor deposition (CVD) reactor under a high temperature around 1000°C, when high-purity electronic grade (>99.9999%) Si is produced through converting SiHCl3 to Si and forming HCl (hydrogen chloride) as a new compound:

SiHCl3  +  H2  →  Si  +  3 HCl

Meanwhile, some byproduct such as SiCl4 (silicon tetrachloride, also known as STC) may form in the CVD reactor too. The mixture (SiHCl3, SiCl4, H2, HCl) leaving the CVD reactor must be separated and recovered as much as possible to meet tight environmental regulations and reduce raw material consumption.

In the first generation process, neither SiCl4 nor HCl is recovered. In the second generation process, only HCl is not recovered. Nowadays close loop production has been achieved in the third generation process, which means all the intermediate products and byproducts are captured and recovered to increase the whole process efficiency remarkably.


Polysilicon process

Polysilicon process example

Polysilicon production challenges

During the process, raw material, intermediate products and byproducts include Si powder, Cl2, H2, HCl, SiHCl3, SiH2Cl2 and SiCl4, therefore valve’s design must be able to deal with these medium, especially the highly abrasive Si powder.

The chemical compounds are extremely dangerous. H2 and SiHCl3 are easily combustible, HCl is dangerous and extremely corrosive, SiHCl4 is a highly toxic substance that poses environmental hazards, which makes it necessary to recover these substances, and bring them back into the production process. Handling these chemicals, including the safe and environmentally sound disposal as well as emission control at the same time is not easy. All these chemicals should be captured and recovered to decrease raw material consumption and increase the whole process efficiency.

SiHCl3 production is a complex reaction equilibrium system, different products and by-products form in the fluid bed reactor. Reaction condition should be controlled precisely to maximize SiHCl3 yield.

Health, safety, environment

Valve leaking poses both an environmental and safety issue due to risk of fire, toxicity and volatility of gases. Emergency shutdown and on/off valves must be able to perform their action in a process or equipment failure. 

Top-class products at maximum yield

The market calls for clean products and high quality. It is important that the process is stable, flexible and under control. Proper valve performance in fluid bed reactor, CVD reactor and recovery system improves the accuracy of throughput control and adversely affects to the plant performance and also the downstream processes. 

Maintenance costs

Valves play an extremely important role in successful polysilicon producing performance. Poorly performing valves in the process must be serviced because they will have a direct impact on the efficiency of the process. 

Plant run-time

Silicon plants are looking for longer plant run-times since downtime means production losses and is a remarkable cost including maintenance costs. This requires reliable equipment.

Reliable valves for polysilicon process

We are all tuned up to answer these challenges through our polysilicon application experience and product offering for control, safety and automated on/off duty that ensure high valve performance. Neles valves have proven performance history and are designed for efficient and reliable process operation.


We are the only single source emergency shutdown valve supplier who has the experience and knowledge to combine intelligence with most reliable valves and actuators. Technology selections like rotary stem operation and inherently fire safe design ensure that latest emission and fire safety standards can be applied. Reliable valves with first intelligent, SIL3 approved safety valve controller and partial stroke testing system Neles ValvGuard™ will ensure that plant emergency shutdown valves will always perform properly when needed.


Throughput losses and poor control performance will be avoided with high performance rotary valves. Flow through the process unit may be changed as the need arises with rangeability of 150:1 and further with full bore ball valves. Our advanced intelligent digital valve controllers for control, on-off and ESD applications ensure high positioning accuracy and fast response. Correct valve selection and sizing with our Nelprof™-program we can assure the best valve performance and process control.


Simple rotary designs, same face-to-face dimensions, and global service network and inventory management will help you to optimize your maintenance activities. Rotary valves have been in service for several years without requiring maintenance and show no sign 
of leakage. The proven performance of Neles valves with long lasting metal seat tightness and shut-off capabilities makes them an ideal solution for on-off, control and critical catalyst handling applications.


Valve performance trend data collected by our smart valve controllers and analyzed by open FDT/DTM technology based configuration and condition monitoring software, makes it possible to predict and respond to maintenance requirements and reduce unscheduled downtime. This gives full transparency to the valve performance in process control.

Chlorine and hydrogen addition valves

Jamesbury™ 9000 series soft-seated ball valve with Xtreme™ seats and live loaded packing has proven to be the right choice as chlorine and hydrogen addition valves. The patented polymeric flexible-lip seat design offers tight shut-off in either direction and extended cycle life with minimum maintenance. Xtreme is a unique material that resulted from a technological break-through in our polymer research lab. The stem sealing design is made for long term and high cycle life that meet highest environmental requirements in a most economical way. Jamesbury 9000 series provides superior quarter-turn performance.

Abrasive powder applications

Neles metal seated ball valve X-series equipped with pneumatic B-series actuator, and intelligent on-off valve controller Neles SwitchGuard™ (SG9000) is an option for the most critical applications. Neles dust proof seat has proven to be the right choice as high erosion application such as silicon powder addition valve. The seat prevents silicon powder from penetrating behind the seat and seizing the valve, and its anti-abrasive feature makes it a perfect choice for silicon powder.