MITIGATION OF SILICA SCALING FROM DIENG‘S

GEOTHERMAL BRINES USING Ca(OH)2

Proceedings Indonesia International Geothermal Convention & Exhibition 2015

Jakarta Convention Center, Indonesia – August 19th – 21th 2015

Hendrik Panthron P.M. 1

Daniel Alfredo 1

Indra Perdana 1,2

Co-author:Author :Felix Arie Setiawan 1

1 Dept. Of Chemical Engineering, Faculty of Engineering, UGM2 Geothermal Research Centre, UGM

Department :

INTRODUCTION

The Fact,

Although the output rate of Dieng geothermal power plant is 60 MW, recently it operates around 42 MW. The prime cause of this low output is the stoppage of injection pipe caused by silica scaling.

SILICA SCALINGPROBLEM!

1. Acidity or pH2. Temperature3. Solubility degree4. Ionic strength5. Presence of nucleating species6. Turbulence of fluid flow

Factor that influence silica scaling

No. Technique Advantages Disadvantages

1 Seeded precipitation

well known in geotermal management produces a solid that is predominantly silica

and allows relatively easy disposal

does not reduce concentration below silica saturation without metal addition

pH control required2 Electrocoagulati

on suitable for colloidal and reactive silica less sludge producion than other precipitation

techniques logistics for delivery of anode than other

coagulation chemicals

high capital investment aluminium residual must be controlled

3 Low pH 4 RO operation

high recovery possible highly suitlable pH for acid mine drainage low pH operation is suitable where acid readily

available

batch operation not yet commercial pH shift not suitable for highly

buffered water4 Causatic

preciptation high recovery proven greater efficiency for silica removal than lime

lesser need for coagulant addition ,reduces sludge formation and complexity

no calcium residual to manage

greater expense of caustic compared to lime

some sludge produced pH shift not suitable for highly

buffered water5 Lime

preciptation high recovery proven well established water treatment technique

pH shift not suitable for highly buffered water

significant sludge production , chemically complex

METHODOLOGY

FLOWCHART

Prepartion• Weigth Silica

Seed• Brine Preparation

Silica Reaction• Temperature

Conditioning• pH Conditioning• Precipitation with

Seed Addition

Silica Analysis• Molybdate 100

g/L preparation• H2SO4 1.5 M

Preparation• Silica Contain

Measurement

Sedimentation

RESULTS & DICUSSION

Figure 2. Dissolved silica concentration in sample at 25oC

Figure 3. Dissolved silica concentration in sample at 50oC

Figure 4. Dissolved silica concentration in sample at 70oC

CONCLUSION

1. With addition of calcium hydroxide, the acceptable SSI value is reached either at pH 9 at all investigated temperatures or temperature of 70°C at all investigated pH levels.

2. Experimental results indicated that the rate of sedimentation of the resulting slurry from reaction at pH 8 and 50°C offered better properties compared to at other conditions.

3. In addition, calcium silicate compounds resulted from the precipitation and sedimentation of silica containing geothermal brine might offer high value added side products in geothermal plant.

Conclusion