Low Pressure Ejector Testing


Date: 3/12/11

 

Purpose:

Test ejector performance when driven by a DC blower to allow off-grid start up.

Ejectors have the significant benefit of having no moving parts and robustness to gas quality.

 

Description:

A series of quick tests were conducted to determine the static vacuum created by ejectors with various entrainment pipe lengths, entrainment pipe diameters, and motive jet diameters with a 24V DC vacuum blower (#BL16).

 

Results:

BL16 Blower Characteristics:
Power: 25A at 24V (600W)

Vacuum: 69 inH2O

 

 

Jet Diameter [in] Entrainment Diameter Entrainment Length [in]
Static Vacuum [inH2O] Comments
0.25 1 1/2" NPT 1.5" 0.25 Plastic jet taper
0.25 1 1/2" NPT 5.75" 1.25 Plastic jet taper
0.25 1 1/2" NPT 17" Coupled 1.75 Plastic jet taper
0.25 1 1/2" NPT 8" 2.5 Plastic jet taper
3/8" NPT 1 1/2" NPT 5.75" 3  
3/8" NPT 1 1/2" NPT 8" 3.5  
1" NPT 1 1/2" NPT 8" 3.5 Using 1"-1 1/2" reducing T
3/8" NPT 1 1/2" NPT 17" Coupled 3.75  
0.2 3/4" NPT 5.75" 4 Smaller plastic jet taper
3/4" NPT 1 1/2" NPT 8" 4.5 Using 1 1/2" T and bushing
0.25 3/4" NPT 8" 8 Plastic jet taper
0.25 3/4" NPT 1.25" 9 Plastic jet taper
0.25 3/4" NPT 4.75" 9.75 Plastic jet taper
0.25 1/2" NPT 3.5" 12

Using reducing T and bushing for converging section

 

The highest static vacuum produced in the tests was with a smaller constriction than the standard GEK ejector (1/2" NPT). For larger entrainment tubes, relatively long lengths improved suction, while reduced performance was seen in the realm of 5" entrainment length with a 3/4" diameter. Using 1 1/2" NPT tube for the entrainment yielded low static vacuums (the highest being 4.5 inH2O). The 0.25" diameter jet consumed around 300 lpm of motive air (18 m3/hr).

 

Discussion:

Results with these tests yielded ejector performance below what we'd like to see in order to start the reactor effectively.

There are three primary considerations with the gas driving system performance:

Vacuum

Flow rate

Motive air at flow

Blower power consumption

 

Our desired performance:

10 inH2O vacuum at 10 m3/hr gas with motive air consumption below 10 m3/hr (below stoichiometric for producer gas).

Since vacuum will drop with gas flow, a static (no flow) vacuum of at least 15-20 inH2O is likely required to merit exploration of ejector gas flow performance.

 

Results from these tests seem to indicate that an ejector driven by this blower will not meet our desired performance specs.