Powergen Bangkok 3 rd October 2103 Session 5 Intake, Cooling and Blowdown Treatment Considerations Cooling Tower Blowdown Treatment and Reuse in a Coal Fired Power Plant in India - Reducing the water footprint in coal fired power plants - Author: Deepak Kachru - Senior Manager Sales Speaker: Simone Callioni Business Development Manager Eastern Aquatech Systems Asia Pvt. Ltd., Pune www.aquatech.com
Contents Introduction Typical power plant WBD Overview of current practice Cost benefit Integrated ETP-WTP concept for a power plant Cost benefit Conclusion
Introduction A coal fired power plant of 1000 1300 MW would normally require about 60 80 MLD of water considering a COC of 5 6 This translates to a specific water consumption of about 2.5 3.0 litre per unit of power produced. This is because of several steps initiated by power producers to reduce their water footprint by proactively maximizing reuse within the plant in ash handling, coal handling and other applications. Final waste from a coal fired power plant can be typically pegged at 120 litres/ Mwh. The present paper intends to highlight, the possibility of re-using the power plant effluent for more critical applications like boiler feed, Evaluate the benefits of such an approach
Current Water Conservation Practices Specific Water Consumption in Power Plants Power plant type Range M 3 /MWh Gas based power plants 1.2-1.7 200 MW coal based thermal power plants 3.5-4.5 500 MW coal based super thermal power plants 3.0-3.5 200 MW coal based power plants with ash water recycling 500 MW coal based super thermal power plants with ash water recycling Bulletin of energy efficiency, Volume 7, Issue 3, December 2006. 3.0-3.5 2.5-3.0
Typical Power Plant WBD Surface Water 3333 clarified water 150 15 to ETP 125 Evap Losses 100 RAW WATER RESERVOIR DM Plant Based WTP 135 3233 RO Based ETP 25 to Ash handling system RO Reject 25 CLARIFIER 3218 160 Waste 15 145 sludge C.O.C = 5 Recirculation rate = 156000 DM TANK Condenser Cooling Auxiliary Cooling Ash Handling System Coal Handling System 135 Regen waste to ETP 5 ETP treated water for reuse as CT make up 100 5 CPU Regeneration 40 400 CLARIFIED WATER TANK 100 10 to ETP 60 to ETP 218 - WTP (150) and Cooling/ventilation and Service water usage (68) Cooling Towers Boiler Blowdown 50 110 Drift 10 Make up & chemical feed, etc. 3000 CT Make up Evap. Losses 2500 CT Blowdown 450 Recycled effluent 100 Power Cycle 10, Hydrogen Generation plant
Current Water Conservation Practices A significant water reuse maximization is currently being practiced in coal fired power plants, with key areas for reuse being, Ash handling, coal handling and CT make up. In the WBD Almost 90% of CTBD of 450 m3/hr combined with BBD of 50 m3/hr can be reused in wet ash system. This translates to an equivalent reduction in usage of fresh water. The residual wastewater to ETP is further treated through a membrane based process and almost 75-80% of the water so produced is reused to augment CT makeup. This still leaves close to 20 30% of concentrated wastewater, which then needs to go through an evaporation process either natural or thermal to achieve zero liquid discharge.
Cost Benefit Around Current Practice Source Quantity, m3/day Cost/m3, INR Cost per day, INR Fresh water 2400 1 15.00 2 36,000 Recycled effluent 2400 13.00 3 31,200 Net Savings in water costs, INR/ day Net savings in water costs, INR/ year Impact of Improvement in COC in cooling tower Reduction in fresh water requirement m3/ year 4,800 (80 $/day) 17,52,000 (29,200 $/year) NIL 4 876,000 Note 1. Fresh water off take will be reduced to the extent of wastewater being recycled for CT make up. 2. This per m3 rate is considered based on applicability of a cess for withdrawal of water from natural sources including pumping and treatment cost upto CT make-up. 3. This per m3 treatment rate is considered based on a membrane based ETP incorporating UF-RO treatment and operating at a maximum efficiency of 75 80%. 4. The permeate quantity from RO is only 100 m3/hr, which is only 3.2% of the total make up water requirement thereby making a negligible impact on COC in cooling tower.
Integrated ETP-WTP Concept An integrated scheme across the ETP-WTP tries to maximize the value proposition of the ETP by not only maximizing throughput but also utilizing it for a boiler feed application instead of CT make up. Essentially the wastewater from the power plant, to the tune of 125 m3/hr (as shown in WBD) is pushed through a recycle system, to condition the water making it suitable for feeding to a polishing MB and then for boiler feed. This in other words means that adopting an integrated scheme with maximum recovery will eliminate the need for a separate WTP dedicated to produce BFW (Boiler feed water).
Integrated Scheme FRESH WATER Cooling Tower Make-Up CURRENT WTP DEMI WATER Integration Cooling Tower Make-up Wastewater ETP Discharge FRESH WATER Cooling Tower Make-Up INTEGRATED Focus on optimizing the water management - Quantity - Recovery - Quality - Purpose Wastewater DEMI WATER Production & Integration Cooling Tower Make-up ETP / WTP Discharge
Integrated ETP-WTP Concept Better understanding the challenges and constraints of utilizing wastewater for critical boiler feed applications requires an overview of the CTBD analysis the major component of wastewater from a power plant. Constituents Units Value Flow m3/hr 125 ph 8.0 Turbidity NTU 1 TSS ppm 104 Ammonia as NH4 ppm 0 Potassium as K ppm 14 Na as Na ppm 502 Mg as Mg ppm 47 Ca as Ca ppm 126 Sr as Sr ppm 0 Barium as Ba ppm 0 Total cations ppm 688 Carbonate as CO3 ppm 3 M Alkalinity as HCO3 ppm 617 Nitrate as NO3 ppm 8 Chloride as Cl ppm 485 Fluoride as F ppm 1.37 Sulphate as SO4 ppm 96 Barium as B ppm 0 Total Anions ppm 1210 Calculated TDS ppm 1900 Constituents Units Value Silica as SiO2 ppm 90-100 Carbon dioxide as CO2 ppm 3 BOD ppm 19 COD ppm 132
Integrated ETP-WTP Concept The previous table indicates the following parameters as critical to the design of an integrated ETP-WTP operating at high efficiency, Total hardness Silica Alkalinity Trace organics And in some cases even oil & grease. From the above list it is imperative to understand that the above contaminants can be addressed in a low efficiency conventional membrane recycle process done by physical removal of these contaminants. This would however involve use of higher chemical dosages of lime, dolomite, and proprietary antiscalants. Having done that will yet, offer a recovery across the system of not more than 80% in the best case.
Integrated ETP-WTP Concept In the Integrated Approach, instead, the main objectives are: 1. maximize recovery 2. utilize the water so recovered for boiler feed, thereby eliminating the need for a separate WTP Following this purpose: 1. a high efficiency process pushes the recovery to over 90% across the membrane based recycle system (achieved by operating the system at a higher ph), ensuring that most of the contaminants are addressed without extensive chemical and or precipitation requirements. 2. the main aim of the recycle system is to produce Demi Water
The Integrated Scheme A typical WBD for the scheme is indicated in below, highlighting the stages of treatment in the scheme and the overall recovery across the system.
Approaching Zero Liquid Discharge It is evident that maximizing recoveries across membrane recycle systems augurs well for any downstream evaporation process, whether based on natural or thermal evaporation. In other words enhancing the recovery across the recycle system from 80% to 90% halves the requirement of water to be evaporated; in a natural or solar evaporation pond, this translates to a reduction in area requirement by 50% and in case of a thermal evaporation system, this would essentially reduce the sizing requirement by half. As a consequence, this translates to a further benefit of the integrated approach: maximizing the recovery makes the solution sustainable and makes easier and viable an ultimate Zero Liquid Discharge arrangement.
Cost Benefit Around Integrated Scheme Source Quantity m3/day Cost/m3 INR Cost per day INR Fresh water 3600 1 15.00 54,000 Impact of reduction in DM plant 2400 2 13.00 3 31,200 opex due to elimination of WTP Recycled effluent 3240 22.00 4 71,280 Net Savings in water costs 13,920 (232 $/day) Net savings in water costs 51,00,000 (85,000 $/year) Note 1. DM plant feed requirement of 150 m3/hr for an output of 135 m3/hr of DM water. 2. This per m3 treatment rate is considered based on a membrane based WTP incorporating UF-RO treatment due to presence of colloidal silica and TOC in fresh water, and operating at a maximum efficiency of 75 80%. 3. DM plant output of 135 m3/hr. 4. This per m3 treatment rate is considered based on membrane based ETP with high efficiency of at least 90% across RO, followed by a 2 nd Pass RO system and a Mixed bed polisher.
Cost Benefit Around Integrated Scheme Achieving an ultimate optimization of the overal water consumption and consequent environmental impact Impact of reduction in size of evaporation pond / system Reduction in overall water requirement m3/ year Benefit to be assessed 1,200,000
Conclusion It is evident from the above discussion that an integrated scheme combining ETP & WTP into a single unit offers the following advantages. Lesser fresh water off take. A significant saving when compared to current recycle practice. Thereby reducing the specific power consumption of the facility. Savings in the operating cost of the water system as compared to the practice of recycle to CT make up. Significant advantage in case of zero liquid discharge requirements from the facility, by reducing the net inflow to the evaporation system being envisaged.
Conclusion In other words with increasing water costs and scarcity, it is important to innovate and adopt schemes that are capable of further reducing the water footprint of the power plant. By using less water and doing it the right way will only mean more savings and provide a significant value proposition to the end user in adopting recycling and zero discharge concepts into the water balance of the power plant.
Thank You For Your Attention Simone Callioni S.No. 244/2, Rajiv Gandhi Infotech Park, Hinjewadi, Pune 411 057 India. callionis@aquatech.com