REC Silicon's fluidized bed reactor (FBR) process

Our new silicon purification process, utilizing a Fluidized Bed Reactor (FBR), lowers the cost of making solar products and saves large amounts of electricity.


Photovoltaic solar energy is widely available and environmentally friendly, and REC Silicon has taken this one step further.  The FBR technology uses significantly less energy for producing high purity silicon used for high performance solar products.

REC Silicon has developed the unique Fluidized Bed Reactor (FBR) silicon refining process, a next-generation method of refining silicon. With the FBR process, we can produce solar-grade silicon at a lower cost, while using 80-90 percent less energy than the traditional Siemens method for converting silane gas to high purity silicon.  REC Silicon is in high-volume production of NextSiTM granular polysilicon using the FBR technology at our Moses Lake plant in Washington, USA. 

 

FBR

SIEMENS

 

 

  • Continuous production
  • Energy efficient
     
  • Batch process
  • Higher energy consumption

 

Reducing energy consumption

A major part of the energy consumption associated with producing solar cells is related to the purification of silicon. This is a challenge, given the rise in both global environmental concerns and energy consumption.  The Siemens process, which is used by most of the industry including REC Silicon, can basically be described as superheating silicon gas and seed rods inside a giant refrigerator. In this method, a gasified silicon compound, being either silane gas (SiH4) or trichlorosilane (SiHCl3) is released into a superheated chamber that contains seed rods of silicon. The heated gas deposits pure silicon on these heated rods, and at the same time the chamber walls need to be cooled in order to avoid silicon deposition on them. Obviously, this process has a large fraction of “unproductive” energy consumption per unit of silicon produced.

With the Fluidized Bed Reactor process, REC Silicon has taken a major step forward in silicon purification using less energy.  Instead of using seed rods, FBR uses seed granules of purified silicon.  The seed granules are fed into a chamber that has heated silane gas entering from below and exiting above. The flow of gas “fluidizes” the silicon granules, causing them to flow like a liquid, as the silane gas breaks down and deposits silicon layers on them. The granules grow larger and heavier and exit when they are sufficiently large. As they do so, new seed granules and gas are introduced into the chamber and the process continues.

FBR is more efficient for several reasons. Firstly, it does not waste energy by placing heated gas and silicon in contact with cold surfaces. Secondly, it produces more silicon per cubic meter of reactor space because the silicon crystals have a larger total surface area than the rods used in the Siemens process. Thirdly, it is a continuous process rather than a batch process so there is less wasted downtime or setup effort required.  And finally, unlike the Siemens process which requires the breaking of  polysilicon rods, FBR granular is harvested in a ready to use form.

Improving Cost of Ownership

FBR offers another major advantage over traditional Siemens polysilicon: reduced cost of ownership.  FBR granular polysilicon is packaged in bulk containers, greatly increasing logistics efficiency.  Granules are round and can flow freely thus enabling automated material transport and crucible loading.  The granular silicon also enables process efficiency such as maximizing crucible load weight that significantly increases productivity.  These factors combined amount to a significant reduction in the cost of solar ingot manufacturing compared to the traditional method further reducing the cost of solar energy.