70    PERFORMANCE EVALUATION AND ECONOMIC ANALYSIS
OF PRE-LIMING AMMONIA STEAM STRIPPING FROM
COKE-PLANT EFFLUENTS
J. J. Ganczarczyk, Professor
Department of Civil Engineering
University of Toronto
Toronto, Ontario M5S 1A4
R. M. Chin, Engineer
Ontario Ministry of the Environment
Toronto, Ontario
M. J. Kelleher. Engineer
MacLaren Plansearch
Toronto, Ontario
INTRODUCTION
Coke-plant effluents contain free and combined (fixed) ammonia. The free ammonia may be
stripped out by application of steam, but to strip combined ammonia, an alkalization of the wastewater, usually by the addition of lime, is required. The fate of ammonia nitrogen in the treatment of
coke-plant effluents is presented in Table I. Poor performance of stripping facilities is caused by
several factors such as fluctuation of wastewater flow to the still, insufficient alkalization, insufficient steam flows, and others. To obtain satisfactory performance of ammonia stripping, proper
design and operation of stripping facilities is required. To achieve an advanced performance, in
addition to the above requirements, an improved process control is needed.
TECHNOLOGY OF AMMONIA STEAM STRIPPING
Ammonia steam stripping from coke-plant effluents is based on Henry's law and is performed in
stripping towers (stills). The effectiveness of the operation depends on the applied hydraulic loading
rate (mass flux), the steam-to-liquid ratio, and the treatment time (stripping tower heights and
number of trays in the tower).
The following general types of stripping systems can be considered.
- application of a stripping still with a free leg only,
- application of a conventional free-and-fixed leg still (conventional liming system),
- application of a pre-liming system, and
- application of a modified pre-liming system.
Table I. Fate of Ammonia Nitrogen in Treatment of Coke-Plant Effluents 11-31
Concentration
 (mg/L)
Raw Wastewater 3,000
After Stripping of Free Ammonia 1,500
After Stripping of Free and Fixed Ammonia
Poor Performance 300
Satisfactory Performance 100
Advanced Performance 30
After Biological Dephenolization 70-150
After Biological Nitrification > 1
597