CHAPTER 3: METHODOLOGY
3.5 Paddy residue co-firing in existing coal power plant
3.5.2 Rice straw co-firing at existing coal power plant
188.8.131.52 Inventory analysis
This section explains how the collected data were adapted to the LCA model and gives details on assumptions that were made. The inventory data were compiled using the Open LCA Framework. However, certain data were cited from some international database such as United State Inventory Database, Australian Database and SimaPro software programme. Rice straw power generation in Malaysia is still under research development. Currently Malaysia is generating electricity using rice husk for own consumption but the consumption of rice straw as a fuel is still in planning board.
Therefore, the data for rice straw combustion used is from wood combustion.
Development of rice straw co-firing with existing coal power plants is not
commercialized yet even though other biomass resources, like wood chip are already in commercialized state. About 77 power plants across the world apply the wood co-firing technique with output capacity between 20 MW to 2035 MW (IEA, 2009b).
(a) Paddy production
Malaysia’s paddy plantations are planting two times a year, categorized into off season and main season. However, there is no significant difference among the tillage energy, fertilizing energy and harvesting energy between both seasons (Bockari-Gevoa et al., 2005). This study used the average data to indicate both seasons. Mechanical field operation data are derived from fuel consumption from land preparation machinery, plant protection machinery and harvesting machinery.
(b) Rice straw collection
Rice straw collection after harvest paddy residue could be accomplished by the use of baler machine and tractor. The data were taken from five sites of rice straw collection in the Northern region of Malaysia. This area uses field baling technique with push-type baler. Each baler can produce bales weighing about 450 kg each. After harvesting, rice straw must be dried for baling process, normally two to three days after harvested. Rice straw are taken when the water content of the straw is less than 25% (Kadam et al., 2000).
In this study an SGR ratio of 0.75 (Butchaiah Gadde et al., 2009) is used to estimate the straw residue yields per area through equation 3.22.
Based on the availability of rice straw according to the nearest availability supply of rice straw, the most suitable co-firing coal power stations are Kapar Power Station and Manjung Power Station. Logistic analysis are related to the spatial distribution of rice
straw for which a contant distribution over the circular catchment area is assumed with the power plant at the centre (Delivand, 2011). The optimization of rice straw area served and radius distance are estimated using equation 3.23 (Delivand, Barz, &
Gheewala, 2011). This is a common application in many other studies (Delivand, 2011;
Kadam, 2000; Dornburg, 2001; Caputo, 2005 ;Bakos, 2008).
(SY× nC× AF × FF
Both the coal power plants are situated near the sea. The availability factor of paddy farm is assumed to be 25% (deduction of 50% sea, and 25% of infrastructure condition).
Farmland factor of 50% due to the weather condition which may cause inaccessibility to collect the rice straw is also applied. The collection efficiency is estimated at 40%
Rice straw fired alone at the Manjung Power Station is unable to be achieved due to limitation of rice straw supply. The electricity generated from rice straw is calculated using equation 3.24 (Qin et al., 2006). HHV employed in this analysis is 14.71 MJ/kg (Calvoa et al., 2004) and NPHR for rice straw fired alone is 17.4 MJ/kWh (Qin et al., 2006). The average electricity generated from rice straw fired alone is 3.92 GWh. The rice straw co-firing needed is calculated using equation 3.25. Boiler loss is determined by equation 3.21.
QELEC=QRS/NPHRRS=HHVRS× WRS/NPHRRS(3.24) RRS=HH VRS× WRS ,CO/HHVCO×WCO(3.25)
Availability of rice straw to co-fire with coal was up to 30% ratio for north region and 20% for central region.
(c) Rice straw transportation
Bale rice straw was applied to analyse transportation sector. Two transportation paths considered were paddy production (PP) to the collection centre (CC) and the CC to coal power plants. Transportation emissions was calculated using the GHG Emissions from transportation or mobile sources, Version 2.3 software (Protocol, 2011). Paddy production to collection centre route is considered for 1 tonne lorry capacity that occupies 2 bales rice straw per lorry. A small size lorry is use due its better convenience to transmit through small road with short distance.
It was assumed that lorry with a capacity of 1.5 tonne was used for moving rice straw from paddy production to collection center as most of vehicles used to transport paddy in Malaysia is between 1 to 3 tonne load capacity (Abdullah, 2006). Transportation of rice straw from the collection centre to existing coal power plant (MP/KP) is using the truck with size 40’8’. Truck transportation would be the most feasible option in the residue collection systems, since trucks have a high degree of mobility (Kadam et al., 2000) . Transportation of rice straw from paddy production to the coal power plant, in Malaysia, modelled according to the routes, the type of transport and distances shown in Table 3.13.
Table 3.13: Average hauling distance for the two studied region Region Path Lorry /Truck Average Hauling Distance, km
North PP → CC Lorry 1.5 tonne 17.77
CC→MP Truck 40’8’ 314.90
Central PP→ CC Lorry 1.5 tonne 15.99
CC→KP Truck 40’8’ 104.30
(d) Power generation
The environmental impact relevant to the rice straw co-firing were taken from the US LCI database based on wood waste combustion and inventory data from Ecoinvent. The analysis of co-firing rice straw uses equation 3.26 to obtain the amount of rice straw needed for electricity generation. Both coal power plants are situated near the sea, so the availability factor of paddy farm was assumed to be 25% (that includes a deduction of 50% for being located by the sea and a deduction of 25% for infrastructure condition).The farmland factor was estimated at 50% due to weather conditions that may cause inaccessibility to collect rice straw. The collection efficiency estimated is 40% (Petrolia, 2008). Availability of rice straw to co-fire with coal was a 30% ratio for the north region and 20% for the central region.
Figure 3.12 shows the flow diagram of coal life cycle when used in electricity generation. It is used to analyse the life cycle assessment of dedicated coal based electricity generation, in order to make the comparison between co-firing with rice straw and coal alone based electricity generation. The data taken from US LCI database and inventory data from Ecoinvent referred to bituminous coal electricity generation at power plants. The relationship for electricity generation and coal needed for electricity generation can be examined using equation 3.26. The applied parameter is based on Manjung Power (MP) Plant technical characteristics (Salim, 2004).
Figure 3.12: Flow diagram of dedicated coal based electricity generation life cycle