GHG Emission Reduction Initiative at Darajat
Greenhouse Gas Emission Reduction Initiative Programs at Darajat Geothermal Plant
Star Energy Geothermal Darajat II, Limited
Sentral Senayan II, 25th floor. Jl.Asia Afrika No.8, Jakarta 10270. Indonesia
Note: this paper has been presented and submitted at 7th ITB International Geothermal Workshop 2018
Most scientists now agree that human activities such as energy usage for electricity and transport come from fossil fuel and deforestation which are largely responsible for climate change. Since the dawn of the Industrial Revolution, climate change have risen sharply include increasing concentrations of Greenhouse Gas (GHG) emission. The GHG caused the earth to heat up by trapping the sun’s heat in the earth’s atmosphere and will cause global climate change to be warmer. This called the greeenhouse effect.
Darajat geothermal power plant consist of a conventional geothermal condensing steam turbine generator with a capacity of 270 MW. Darajat geothermal utilises a direct steam expansion turbine from the geothermal field steam supply. It has no supplementary firing for additional steam supply to generate electricity.The GHG emission mainly from steam supply that contains carbon dioxide (CO2) and methane (CH4). Eventhough geothermal power plant have smaller emission compared to fossil-fuel based power generation and coal-based electricity generation, some initiative programs to reduce GHG were taken as part of company commitment in resources utilization through energy efficiency program.
Some initiative programs are: Clean Development Mechanism (CDM) program, cooling tower direct drive installation, PCV debottlenecking installation, substitution of fluorescent lamp with Light Emitting Diode (LED) lamp at office building and general area, substitution of High Pressure Sodium (HPS) lamp with LED light and photocell installation, steam well workover, and Unit I upstream pressure reduction. Total GHG emission reduction program on 2016 are 1,306,100 ton CO2 equivalent with absolute intensity 0,7544 ton CO2/MW.
Keywords: Greenhouse Gas, Geothermal, Emission Reduction, Darajat
In 2000, Southeast Asia region (including Indonesia) contributed 12% of the worlds GHG emission, amounting to 5,187 MtCO2 equivalent, which is increasing 27% compare to 1990. The land use change and forestry sector was the biggest source, contributing 75% of the region’s total, the energy sector 15% and the agriculture sector 8%. There is considerable scope for mitigation measures that can contribute to a global solution to climate change and bring significant co-benefits to Southeast Asia. Although Southeast Asian countries together contributed about 3.0% of global energy-related CO2 emissions in 2000, this share is expected to rise significantly in the future given relatively higher economic and population growth compared to the rest of the world, if no action is taken.ADB, 2009
Mitigation strategies are available and taken by Southeast Asia region in both the energy supply and demand sectors. On the supply side, options include efficiency improvements in power generation, fuel switching from coal to natural gas, and the use of renewable energy including biomass, solar, wind, hydro and geothermal resources. On the demand side, the key sources of GHG emission are the residential and commercial building, industry, and transport sector. In industry sector, several key options such as use of more efficient motor, more efficient end-use electrical equipment, improved management practices (energy audit and benchmark), heat and power recovery, fuel switching, wide array of process-specific technologies, and material recycling and substitution. (ADB, 2009)
Renewable energy accounted for over 15% of world primary energy supply in 2004, including traditional biomass (7-8%), large hydro-electricity (5.3%, being 16% of electricity generated), and other new renewables (2.5%). In 2005, the geothermal sector accounted for 0.4% of total supply.Under the business as usual case of continued growing energy demand, renewables are not expected to greatly increase without continued and sustained policy intervention. (IPCC, 2007)
The use of renewable energy in Indonesia is still limited. Presidential Decree No.5 (2006) has set the goal of increasing the share of renewable energy (biomass, geothermal, wind, solar energy, and others) and new or clean energy such as nuclear power or hydrogen to 15% of the primary energy mix by 2025. As part of this initiative the Ministry of Energy and Mineral Resources Decree
1122/2002 for small-scale energy generating installations and Decree 02/2006 for medium-scale energy generating installations mandate Indonesia’s national public utilities to purchase renewable energy generated from small and medium scale installations.
Although Indonesia has significant geothermal resources in the world with its potential 29,544 MW, but the electricity generation from geothermal power plant is currently only 4.87% or 1,439.5 MW from total installed capacity. The primary energy in Indonesia, only 6,2% is from renewable sources include geothermal. While 43.09% of primary energy was from fossil fuel resourcess (EBTKE ESDM, 2016).
In the end of 2015, the capacity of power system Indonesia is 55,528.10 MW and it is 4,64% increase compared to 2014. Geothermal power plant only contributed 2.58% from total capacity of power system in Indonesia (DJK ESDM, 2016).
Darajat geothermal power plant currently operated by Star Energy Geothermal Darajat II, Limited (SEGD), formerly undertaken by Chevron Geothermal Indonesia, Ltd (CGI). SEGD operates under a Joint Operating Contract (JOC) with Pertamina (Persero) and an Energy Sales Contract (ESC) with PT PLN (Persero). SEGD supplies geothermal steam to 55 MW power plant (unit I, owned by PT PLN) and owns and operates a 95 MW power plant (Unit II) and 121 MW power plant (Unit III).
Geothermal energy in Darajat is stored in a steam reservoir within the earth’s crust. Dry saturated steam at high pressure is produced at the surface from wells drilled into this reservoir. The steam is delivered to the power generation facilities through a steam gathering system, to move the turbine blades and drive a generator hence generating electricity. Exhaust steam from the turbine is condensed in a direct contact condenser and approximately 25% of the condensed exhaust steam is re-injected into the geothermal reservoir, with the remaining 75% being evaporated in the cooling tower. This technology is technically sound and environmentally safe as is demonstrated by hundreds of similar installations around the world, including Indonesia (CGI, 2015).
SEGD as one of the geothermal industry in Indonesia have continual improment program to improve performance in environmental aspect. The program is the implementation of SEGD’s commitment not only to meet regulatory requirement, but also beyond compliance to use resources efficiently, reduce emission and prevent negative impact to environment and social aspect.
This research is descriptive qualitative method to describe and explain the GHG emission reduction initiative program at Darajat geothermal power plant by data collection method, review of literature, and interview with Darajat team. The rationale of this qualitative approach was to explore and describe the experiences and perspective of Darajat organization team in implementing GHG reduction program. This study will contribute to the literature on the sources of geothermal project as a lower emission energy sources and its initiative GHG emission reduction program implementation & best practices in contribution to national GHG emission reduction.
Darajat Unit III CDM project has followed methodology ACM0002 ver.16.0 on large-scale consolidated methodology: grid-connected electricity generation from renewable sources. This Darajat Unit III CDM project periodically audited by external parties to get CERs (certified emission reductions) from United Nations Framework Convention on Climate Change (UNFCCC) secretariat. The CERs achieved from this project was published in UNFCCC website and made public.
GHG emission reduction program at geothermal Darajat has been verified by external parties on September 2017 as a process of data evaluation, completeness and objectiveness of data compared to method, procedure and other requirements to ensure the data are accurate and acknowledge to reflect the implementation. The data verification was conducted both in the field and laboratory through document review, interview, field observation, study literature and consultation or discussion with expert team from PT ITS Kemitraan as the independent 3rd party verificator. The verification report is the performance of 4 years period of resource utilization at SEGD. The emission reduction program in this paper is only focus on the 2016 performance result to reflect the latest condition at Darajat geothermal plant.
The GHG emission reduction calculation from the electrical saving program convertion use emission factor at Jawa-Madura-Bali (JAMALI) interconnected grid based on Directorate General of Electricity and endorsed by Indonesia Designated National Authority (DNA) on 17 February 2014 with value 0.814 tCO2e/MWh. The emission factor value is align with the value of updated Darajat Unit III CDM Project Design Document (PDD) approved by UNFCCC on 5 September 2015. This emission factor value will not change for the each crediting period after approved by UNFCCC.
Result & Discussion
SEGD management is committed to reduce both conventional and GHG emission as stated in the Safety, Health, and Environment (SHE) policy signed by President Director as top management in the corporate level. Asset Manager Darajat as top management at Darajat geothermal power plant then made more specific Environmental Policy as well as 5 years strategic plan including in providing budget and resources to ensure the programs are well implemented. The GHG emission reduction program involved interdepartment team member such as Facility Engineering, Operation & Maintenance, Safety Health & Environmental and Resource Management team. The programs were evaluated regularly by management regularly to review the progress.
The GHG emission reduction program implemented by SEGD on 2016 are:
- Darajat Unit III CDM program
Darajat Unit III geothermal project has received endorsement from Indonesian host country on 31 August 2006 and registered at UNFCCC secretariat with reference number 0673 since 11 Dec 2006.
Based on approved 2nd crediting period renewal of PDD, approved on 5 Sep 2015, estimated amount of emission reduction from Darajat Unit 3 geothermal project is 753,136 tons CO2 equivalent per annum. The methodology used was ACM0002 ver.16 – Grid-connected electricity generation from renewable sources with crediting period until 5 Oct 2019 (UNFCCC, 2017).
Project emissions for geothermal power plants are calculated as follows:
|PEy =||Project emissions in year y (tCO2e/yr)|
|PEff,y =||Project emissions from fossil fuel consumption in year y (tCO2/yr)|
|PEgp,y=||Project emissions from the operation of geothermal power plants due to the release of non-condensable gases in year y (tCO2e/yr)|
However, for Darajat Unit III geothermal project, no fossil fuel is used to generate electricity. Darajat Unit III geothermal utilizes a direct steam expansion turbine from the geothermal field steam supply. It has no supplementary firing for additional steam supply to generate electricity. Darajat Unit III geothermal project sharing with another existing unit (Unit II geothermal) have been installed a diesel generator used for back up and emergency purpose only. The methodology does not account CO2 emissions from the combustion of fossil fuel which used for the back up or emergency purpose (this project emission can be neglected). Therefore PEFF,y is not applicable for this project activity
Emissions of non-condensable gases from the operation of geothermal power plants (PEGP,y). The fugitive emissions of carbon dioxide and methane due to release of non-condensable gases from produced steam PEGP,y is calculated as follows:
|PEgp,y =||Project emissions from the operation of geothermal power plants due to the release of non-condensable gases in year y (tCO2e/yr)|
|Wsteam,CO2,y=||Average mass fraction of carbon dioxide in the produced steam in year y (tCO2/t steam)|
|Wsteam,CH4,y=||Average mass fraction of methane in the produced steam in year y (tCH4/t steam)|
|GWPch4,y =||Global warming potential of methane valid for the relevant commitment period (tCO2e/tCH4)|
|Msteam,y =||Quantity of steam produced in year y (t steam/yr)|
The baseline emissions are calculated as the product of the electricity produced by renewable generation unit, multiplied by an emission factor. Tool to calculate the emission factor for an electricity system describes “for determining the electricity emission factors, if the DNA of the host country has published a delineation of the project electricity system and connected electricity systems, these delineations should be used”. The Indonesian DNA has published the latest approved emissions factor on JAMALI grid on 17 February 2014. Therefore, the baseline emissions are calculated as follow:
|BEy =||Baseline emissions in year y (tCO2/yr)|
|EGpj,y =||Quantity of net electricity generation that is produced and fed into the grid as a result of the implementation of the CDM project activity in year y (MWh/yr)|
|EFgrid,CM,y=||Combined margin CO2 emission factor for grid connected power generation in year y calculated using the latest version of the “Tool to calculate the emission factor for an electricity system” (tCO2/MWh)|
Refer to methodology ACM0002: Grid connected electricity generation from renewable sources version 16, since the project is a capacity addition to an existing renewable energy power plant, option 1 is used to calculate the quantity of electricity generated, then the EGPJ,y is calculated as per the formula below:
EGPJ,y = EGfacility,y – (EGhistorical + δhistorical);until DATEBaselineRetrofit
EGPJ,y = 0; on/after DATEBaselineRetrofit
|EGPJ,y||=||Quantity of net electricity generation that is produced and fed into the grid as a result of the implementation of the CDM project activity in year y (MWh/yr)|
|EGfacility,y||=||Quantity of net electricity generation supplied by the project plant/unit to the grid in year y (MWh/yr)|
|EGhistorical||=||Annual average historical net electricity generation delivered to the grid by the existing renewable energy plant that was operated at the project site prior to the implementation of the project activity (MWh/yr)|
|δhistorical||= =||Standard deviation of the annual average historical net electricity generation delivered to the grid by the existing renewable energy plant that was operated at the project site prior to the implementation of the project activity (MWh/yr) Point in time when the existing equipment would need to be replaced in the absence of the project activity (date). This only applies to retrofit or replacement projects.|
In case EGfacility,y < in a year y then: EGPJ,y = 0. Since the facility of Darajat Geothermal power plant consist of three units power plants, three electricity meters have been installed in Darajat facilities to monitor the net electricity generation of each units (Unit I, Unit II, and Unit III). Thus the Quantity of net electricity generation supplied by the project plant/unit to the grid is obtained from the sum of net electricity generation supplied by Unit I, Unit II, and Unit III.
|EGfacility,y =||Quantity of net el,ectricity generation supplied by the project plant/unit to the grid in year y (MWh/yr)|
|EGfacilityI,y =||Quantity of net electricity generation supplied by unit I to the grid in year y (MWh/yr)|
|EGfacilityII,y =||Quantity of net electricity generation supplied by unit II to the grid in year y (MWh/yr)|
|EGfacilityIII,y=||Quantity of net electricity generation supplied by the project unit III to the grid in year y (MWh/yr)|
Emission reductions are calculated as follows:
|ERy=||Emission reductions in year y (tCO2e/yr)|
|BEy=||Baseline emissions in year y (tCO2/yr)|
|PEy=||Project emissions in year y (tCO2e/yr)|
Table 1. Summary of Darajat Unit III CER Issuance
|Category||Cover Period||CERs (tCO2e)|
|Monitoring Report #1 (CER issued on 11 Jun 2009)||14 Jun 2007 – 31 Aug 2007||90,804|
|Monitoring Report #2 (CER issued on 25 May 2011)||1 Sep 2007 – 1 Nov 2008||737,846|
|Monitoring Report #3 (CER issued on 25 May 2011)||2 Nov 2008 – 31 Jul 2009||501,310|
|Monitoring Report #4 (CER issued on 17 Apr 2012)||1 Aug 2009 – 31 Oct 2010||889,337|
|Monitoring Report #5 (CER issued on 11 Dec 2012)||1 Nov 2010 – 31 Dec 2011||838,969|
|Monitoring Report #6 (CER issued on 15 Apr 2013)||1 Jan 2012 – 30 June 2012||362,546|
|Monitoring Report #7 (CER issued on 16 Jun 2013)||1 July 2012 – 31 Dec 2012||345,420|
|Monitoring Report #8 (CER issued on 13 Jun 2014)||1 Jan 2013 – 30 Jun 2013||346,094|
|Monitoring Report #9 (CER issued on 15 Aug 2014)||1 Jul 2013 – 31 Dec 2013||263,040|
|Monitoring Report #10 (CER issued on 4 Dec 2015)||1 Jan 2014 – 13 Jun 2014||322,539|
|Monitoring Report #11 (CER issued on 5 Jan 2017)||14 Jun 2014 – 30 Jun 2015||761,593|
|Monitoring Report #12 (CER issued on 18 Aug 2017)||1 Jul 2015 – 30 Jun 2016||801,111|
Table 1 shows the summary of Darajat Unit III CERs issuance from UNFCCC Executive Board that has been verified by Designated Operational Entity (DOE) which is conducted by Det Norske Veritas (Monitoring Report #1 – Monitoring Report #9) and Bureau Veritas (Monitoring Report #10 – Monitoring Report #12) as approved DOE. Total emission reduction of Darajat Unit III CDM project during period January – December 2016 is 797,981 tons CO2e.
2. Cooling Tower Direct Drive (CTDD)
In the old system, cooling tower using conventional fan motor (gearbox) with electric power according to the specification of the equipment used. This system always operates with a fixed power. The cooling tower fan is useful for drawing cool air from the environment so that it helps in cooling water process.
It is known that by using the old system, the fan motor always operates on the use of fixed electric power. Meanwhile, when the environmental temperature is decreasing especially during the night, the expected cooling water temperature will be more easily achieved and the fan usage can be reduced without affecting the cooling water temperature.
SEGD has reviewed the use of direct drive motor fan, a cooling tower direct direct that allows the application of a control system that controls fan rotation based on cooling water temperature derived from and determined by ambient temperature. If the cooling water temperature has been reached, the fan spin will slow down so that the power used to operate the fan will decrease. If the cooling water temperature has not been reached, the fan spin speed will adjust in order to attract more cold air to assist the cooling process. As a pioneer in the use of this technology, SEGD has purchased two CTDD units mounted on two unit cooling towers of Unit III.
The energy savings are obtained especially when the ambient temperature around the generating unit is lower. Energy savings generally occur during the night when the environmental temperature reaches the lowest point. The lower the temperature of the environment the greater the energy savings can be achieved. The difference between cooling tower conventional fan motor and direct drive motor can be described in the Figure 1.
CTDD uses variable speed drive method (VSD) where motor rotation will be controlled by cooling tower temperature. So that when the night temperature will be lower resulting in motor rotation slows automatically and consumption of electrical energy will shrink. CTDD benefits are significantly improved reliability (5 year warranty, 20+ year rated life), reduced maintenance costs (eliminate oil changes, gearbox refurbishments, alignments, etc.), significant energy savings potential due to variable speed (typical 30-60% energy savings), improved safety (e.g., eliminates “wind milling” issues) and eliminates oil contamination issues (leaking gearboxes).
CTDD installation was completed on 2015 and fully operation in 2016. CTDD able to reduce electrical consumption from 125.32 kW to 113.63 kW without reducing motor performance. Energy saving was calculated from reduction of motor drive power and operation time. On 2016, CTDD installation reduced electrical consumption 85.44 MWh with energy efficiency 9.1% and equal to emission reduction 69.55 tons CO2e.
3. Pressure Control Valve (PCV) Debottlenecking
SEGD performs pressure reduction optimization at the interface area of Darajat Unit II and Unit III power plants. Decrease in pressure at PCV Units II and III are identified as barriers, which, if reduced, can provide economic and operational benefits. The declining in pressure drop has the potential to increase the discharge of existing production wells, thereby reducing the need for drilling of new wells in Darajat field. The debottlenecking process is done by installing parallel PCV in Unit II and Unit III, and separating the headers from the two power plants.
The debottlenecking interface project is one of the best practices of geothermal steam field optimization as part of the surface facility optimization and integrated production system optimization process. The project has demonstrated a good synergy case between surface and sub-surface in identifying and developing debottlenecking efforts for geothermal surface facilities.
The benefits gained by the company through the implementation of this activity is to delay the drilling of wells and expand the capacity of the steam supply to meet the operating targets. In response to changes in reservoir conditions and mode of operation, improvement efforts should be undertaken as a process of integration between Resource Management, Facilities Engineering, and Operation and Maintenance team.
As the Unit III interface pressure is the highest, operation of the Unit III PCV dominates the flow conditions as it sets the common pressure upstream of both the Unit II and III PCVs. Figure 3 shows interface piping post debottlenecking at Darajat.
This first step was to confirm project economics as planned in design phase by reducing the Unit III upstream PCV pressure to 18.3 bar(a). The summary of the first step and the second step result is shown in Table 2 below.
From project economic standpoint, to meet the target of Stage 1 in deferring six (6) makeup wells at the initial 9.3% decline rate, the new system should be able to get 109 kg/s steam gain from lowering WHP. This steam gain target is around 29.6 % of the total Unit II and III steam demand. Overall, the first performance step was able to increase wells deliverability by 34.3% from the initial well production rate, thus exceeded the said steam gain target. This is a clear indication that the project is able to achieve the target improvement of reservoir condition.
Table 2. First and second performance result
|Data||Initial Condition||First Test||Second Test|
|Upstream PCV Press, bar(a)||21.6||18.1||17.8|
|Average WHP, bar(a)|
|Total Steam Rate, kg/s|
This program has minimized pressure loss at PCV interface so that upstream pressure can be lowered and ultimately impacts on the increased availability of steam reserves. Reduction of well pressure up to 1 bar, and increase the availability of steam by 70 kg / s. Construction of PCV parallel installation for Unit II and III was completed on 27 November 2013. Electrical energy saving calculation was from convertion of steam supply become electricity. Steam pressure optimation maintained at interface area is 17.8 barg. On 2016, SEGD successfully increase steam supply to 49 kg/s and equal to total energy saving 10,906.02 MWh with total emission reduction 8,877.5 tons CO2e.
4. Substitution of Flourescent Lamp to LED lamp at Office Building and General Area
The flourescent lamp or tube luminescent (TL) lamp is a long tubular illumination device filled with a noble gas such as argon at a pressure of 200-660 pa that serves to help light the lamp. The mercury in the tube functions in the formation of light. At the time of operation, the time temperature of the lamp is under pressure from mercury. Radiation released by mercury emission is ultraviolet light with wavelength 253-257 nm. The phosphor layer on the tube serves to convert ultraviolet light into visible light so that the intensity of light increases. However, the energy required to emit light from TL lamps requires considerable electricity and is less efficient in its use because some electrical energy is wasted from the lamp in the form of heat energy.
The LED lamps are now popular and widely used although this technology is still relatively new. It can even be said LED lamp at this time has begun to get the attention of the public because it has many advantages compared with other types of lights. With advantages such as cost-effective electricity, environmentally friendly and durable to be the excess of LED lights that cause many parties began to switch to this lamp.
Compared with TL lamps, the use of LED lampss superior to various aspects. LED lamps require less electricity for lighting, with the intensity of illumination comparable to TL lamps. In addition, LED lamps also have a longer operating life than TL lamps, which can reach the age of up to 15 years. Then LED lamps are also more environmentally friendly because it does not contain harmful materials (toxic), such as mercury for the environment and humans. The LED lamps also provide an advantage for indoor comfort, where the light produced by LED lamps does not produce ultraviolet (UV) light and heat energy. In the long term, the use of LED lamps can provide an investment advantage as it reduces the cost of lighting maintenance.
This program is done by replacing the TL lamp to LED lamp with a more energy efficient. The continuous use of LED lamp continues until December 2016 with the target of replacing the TL lamp to LED lamp is 1,512 units from start of 2014. As of December 2016 the replaced TL Lights are 814 Units and the remainder of which has not been replaced are 698 units will be conducted step by step in the future (after existing TL lamp is broken or not functioning). Expected by replacing the TL lamp to the LED lamp can further save energy again. Replacement TL lamp is done throughout the area of Operation and Office locations in the Darajat field and also at Wisma office SEGD in Garut City.
This TL lamp replacement varies from TL 36 Watt lamp to 20 Watt LED lamp (total 1,335 lamps), TL18 Watt lamp becomes 10 Watt LED (total 150 lamp), and 13 Watt TL lamp becomes 8 Watt LED lamp (total 27 lamps). Calculation of emission reduction is from energy consumption reduction times factor emission. On 2016, total energy saving from this program is 13.87 MW or equal to 11.29 tons CO2e emission reduction.
5. Substitution of HPS Lamp to LED Lamp and Installation of Photocell
High pressure sodium (HPS) lamp is smaller and contains additional elements such as mercury, and produces a reddish orange light. Some light bulbs also produce a bluish white light. This may be from mercury light before sodium evaporates perfectly. The D-line of sodium is the main source of light from the HPS lamp, and this narrow spectrum is widened by high pressure sodium in the lamp, because of this widening and the emission of mercury, the color of the illuminated object can be distinguished.
This program is done by replacing HPS Lamp with LED Lights in PGF Turbine Floor. Replacement LED light is coupled with the installation of Photo Cell as a light sensor. This LED light will be on at night and vice versa during the day This light will be off automatically. HPS lamp replacement on turbine floor Unit II of 18 lamps and Unit III of 8 lamps. Total lamp replacement of 26 HPS lamps. HPS lamp which consume energy 250 Watt/pcs will be replaced with LED lamp which consume energy 80Watt. This HPS lamp previously flashed for 24 hours and will now turn the ignition to 12 hours using a light sensor.
The method used in applying the replacement of HPS lamps to LED lamps is the inventory of HPS lamps in the SEGD geothermal operation environment and the replacement of these lamps into LED lights is based on the operating life of HPS lamps. The reduction in electricity usage is calculated based on the number of HPS lamps that have been replaced to LED lamps and the difference in electricity consumption between HPS lamps and LED lamps with the same level of illumination. Calculation of emission reduction is from energy consumption reduction times factor emission. On 2016, total energy saving from this program is 183.63 MW or equal to 149.48 tons CO2e emission reduction.
6. Steam Well Workover
Geothermal fluid is a fluid in the form of vapor or liquid containing various chemical elements, in which the formation process occurs inside the earth (reservoir) under conditions of very high pressure and temperature. In geothermal operations, this fluid will flow by itself through wells from the reservoir to the surface. During flowing in the well, there is a decrease in the pressure that triggers the occurrence of flashing process (the liquid turns to steam). Flashing process that occurs due to the pressure drop will cause the formation of silica precipitate that will stick to the wall of the well.
Silica compounds have several forms: quartz, cristobalite, amorphous silica, chalcedony, etc. Quartz is the most stable form and has the lowest solubility. Silica precipitation generally occurs when the concentration of silica in solution exceeds the solubility of amorphous silica. Silica precipitates are often a problem in geothermal field operations. The presence of silica in the production well tube results in reducing the diameter of the flow surface inside the pipe, thereby reducing the flow rate and the likelihood that the pipe is blocked so that the vapor can not flow to the surface.
Previously, SEGD performs maintenance and repair of wellbore by using surface water and acid chemicals (HCl and HF). Acid chemicals are used to dissolve the silica scale attached to the pipe. The use of these acid chemicals requires special handling from delivery to use. Shipment of chemicals to the geothermal field requires escort from the police. The acid used also has great potential hazards, both for workers and for the environment. In addition, surface water is used as a well cleaner as well as cleaning the residual acid used. Both of these activities require an enormous amount of surface water.
Currently SEGD uses Rotojet Method to maintain and repair wells. The Rotojet method is a method used for maintenance and repair of wells by using high pressure condensate water replacing the use of acid and surface water so that the use of surface water can be reduced. Replacement of surface water with condensate water for well maintenance and repair activities using Rotojet Method is an idea of internal SEGD in realizing water conservation by means of a 2-month trial conducted in 2013 in 6 production wells. The results show that the implementation of the Rotojet Method has been very successful in improving and increasing well production to exceed the estimated target. There is no regulation that requires a company to re-utilize condensate water from production for well maintenance and repair activities by the Rotojet Method. SEGD is a pioneer in the use of Rotojet Method because in general maintenance and repair activities of wells use acid and surface water. However SEGD performs surface water replacement with condensate water. Figure 4 shows rotojet equipment scheme that implemented in Darajat.
The methodology used to determine the amount of surface water use with water condensate substitution as a cleaning medium and the amount of chemical use is by recording the actual data flowrate by the Operation and Production Team. From the well treatment result will be generated increase of steam wells that can generate electricity (MWh).
From the objectives that are expected to be achieved, the goal has been achieved is the increase of well vapor from this activity that is environmentally friendly and energy efficient so that it can also reduce emissions from these activities. The objective of this program is to restore the productivity of geothermal wells through the well maintenance process by cleaning the silica crust using environmentally sound methods. Table 3 shows detail steam produced from each well after workover program.
Table 3. Total steam produced from workover
|Well||Baseline, Sep ’15 (kg/s)||Plan Total Steam Produced (kg/s)||Actual Steam Produced (kg/s)|
On 2016, total energy saving form this program is 613,035 MWh or equal to 499,010.82 tons CO2e emission reduction.
7. Unit I Upstream Pressure Reduction
The program aims to revive and increase the capacity of wells that were previously inferior or unproduced production wells. This program is carried out by setting the pressure wells to lower the upstream pressure of the Unit-1 steam pipeline. Reduced system pressure has an impact on increasing the availability of the steam reserves Unit-1.
The steps of unit I upstream reduction as follow: study on the well head pressures Unit I and interface Unit I as a baseline; analyze potentional additional steam supply by wellhead pressure reduction; create SOP; survey on measurement of geochemical on the gas and well superheat condition; monitor operationability of well after pressure reduction and evaluation process on the program implementation.
The upstream pressure downstream pipeline activity unit Unit 1 achieved the following targets: lowered the pressure by 1.8 bar from the initial operating pressure of 15.8 barg to 14 barg and With reduced steam field operation pressure, production wells may obtain additional production capacity of 20.4 kg / s or equivalent to 10.5 MW.
The program of decreasing the pressure of Upper Pipe Line upstream of Unit-1 successfully reached the target of adding steam supply of 20.4 kg / s or 94,054.74 MWh per year. The environmental impact resulting from this innovation is to delay the drilling of additional wells thus eliminating the potential emission of 676.27 tons of CO2e from the use of 240,000 L of fuel per well on 2015. On 2016, the emission reduction from this activity was not considered as per 3rd party verification report.
GHG emission reduction initiative program at Darajat geothermal plant can be summarized at Table 4. Table 4 shows the absolute reduction and absolute intensitiy of each specific program. With total 1,306,100 ton CO2e and emission intensity GHG emission reduction in 2016, SEGD become 4th position of world benchmarking among other geothermal companies in the world as per benchmarking report by 3rd party conducted by PT ITS Kemitraan with GHG emission intensity 0.0173 ton CO2e/MWh.
Table 4. Absolute result of GHG emission reduction program
|No.||Program||Absolute Reduction (ton CO2e)||Absolute Intensity (ton CO2e/MWh)|
|4||TL lamp to LED lamp||11.29||0.00000652|
|5||HPS lamp to LED lamp||149.48||0.00008635|
|7||Unit I pressure reduction||0||0|
In 2016, SEGD, as operator of Darajat geothermal power plant has implemented GHG emission reduction itiative programs with total absolute emission reduction 1,306,100 ton CO2 equivalent with total absolute intensitiy 0.7544 ton CO2e / MWh.
Darajat Unit III CDM program become the biggest CERs achieved at geothermal sector in the world and contribute in national CERs achievements. PCV debottlenecking, well workover and unit I pressure reduction are some of the best practices of geothermal steamfield optimization to meet operation target without drilling new make-up wells in the Darajat field. Unit I pressure reduction implemented without operation expense budget to optimize the steam supply.
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