Two-Stage Vapor Recovery Units

 R. A. Nichols Engineering Two-Stage VR Unit has a recovery efficiency of 93% of saturated inlet gasoline vapor. The 2-Stage VR Unit emissions are 67 mg/l or 0.164 gal/1000g with saturated inlet gasoline vapor. The systems meet the EPA 80 mg/l standard, no longer in effect, with vapor return from service stations.  In larger terminals, >2M gal/day, serving mandated Service Station Stage I accounts, the system shows higher economic returns than a 1-Stage VRU, both with a Burner.

  2-Stage units are more complicated than the 1-Stage unit, but still much simpler than carbon and refrigeration units. These units have again typically only two motors and various pressure and flow control valves. The two-stage sliding vane compressor has a first- and second-stage compressor with a common motor and the absorber fuel supply pump has the second motor. A 300 cfm system has 120 nameplate hp. Maintenance costs are dramatically lower than any carbon or refrigeration unit in operation as the systems only run when they are processing vapor.

              2-Stage units are very effective for large terminals with Stage 1 and minimal diesel loading.  The advantages of increased efficiency are often outweighed by lower capital cost, simplicity and decreased operating and maintenance costs of the 1-Stage VR Unit. Both single and 2-Stage VR Units use a tail gas burner. Burner outlet emissions to less than 0.5% of inlet vapor volume, less than 5 mg/l, and/or more than 99+% efficiency.