Efficacy and profitability of a mobile grinder system for biomass production in Korea

ABSTRACT

Forest biomass utilization is increasing in Korea, but on-site biomass operations have not been studied much. This study investigates the efficacy and profitability of a mobile grinder system that consists of a mobile tub-grinder, a grapple excavator, and a three-man crew. A time study was carried out to measure production time and to calculate the productivity of the system. The mobile grinder system ran 3 work cycles a day for total of 347.5 minutes. It was only productive for less than half of the 8 working hours a day (237.4 minutes, utilization rate of 49.4%). We estimated that the system produced 246.2 m³/day, which was 26% lower than the daily capacity reported by the grinder operators. This study found the system could make utilizing forest biomass profitable, although this depended on limited market information. The profitability of the system can be improved by increasing work cycles a day and decreasing organizational delays by better operation management. More research is needed to increase the on-site productivity of the system, and incorporate it and the actual price of wood chips to further assess the profitability of the system. The study results can be used as a justification for the grinder system, encouraging forest managers to adapt this relatively new operation.

KEYWORDS:

• Biomass productivity
• economics
• forest biomass
• mobile tub-grinder
• time study

Introduction

Developing renewable energy sources is one of the major challenges of our time worldwide and forest biomass has been recognized as a sustainable energy source which is currently underutilized. Forest residues and previously unmerchantable woody biomass materials can be processed into uniformly sized biomass feedstock and utilized for energy production. This process, in-woods chipping or grinding, is referred as “comminution” (Han et al. 2015). There are two primary machines used for biomass comminution: chippers (disc and drum) and grinders (horizontal and tub). Chippers produce relatively uniform chips by cutting and slicing larger-size woody materials (Assirelli et al. 2013), while grinders reduce the particle size of woody biomass materials by repeatedly pounding and crushing them into smaller pieces (Han et al. 2015). Both chippers and grinders produce relatively uniform biomass feedstock: wood chips. Chippers are better designed to process larger-size materials. Grinders can process a variety of biomass materials, such as whole trees, stumps, tops, brushes, and forked branches, and are less affected by contamination (e.g. soil) (Han et al. 2015).

Subsequently, biomass comminution operations have been increasing and are often preferred on site, either at the roadside (Ghaffariyan et al. 2013) or in a centralized location (Bisson et al. 2016), to at a plant because of the overall high demand on logistics and costs, and often high dust and noise emissions (Kanzian et al. 2009; Röser et al. 2012). A variety of aspects have been studied recently for productivity and efficiency (Röser et al. 2012; Ghaffariyan et al. 2013), time study and delays (Spinelli & Visser 2009), low-price small mobile chipper/grinder (Yoshida & Sakai 2014a, 2014b), transport efficiency (Acuna et al. 2012), system logistics (Bisson et al. 2016), and optimization (Zamora-Cristales et al. 2015).

In Korea, a standing tree volume of 8.7 million m³/year was harvested, and 4.2 million m³/year, which is less than 50% of the standing tree volume, was collected and used as timber (Korea Forest Service 2012a, 2012b). Unused woody material was left on the ground either as part of normal forest management practices (Dukes et al. 2013) or due to economic and operational difficulties (collecting, processing, and transporting costs, and low market value for products) (Kim & Park 2010; Bisson et al. 2016). This unused material could be used as renewable energy source if comminuted and transported. Chip production in Korea is relatively small-scale compared to other countries, although it has been increasing from 356,610 BDT (Bone Dried Ton) in 2010 to 425,760 BDT in 2014 (Korea Forest Service 2015). There are only 10 companies currently producing wood chips (Korea Forest Service 2015). However, little is known about biomass comminution operations in Korea. Mun et al. (2014) studied operational productivity and cost for forest biomass utilization in Korea, and reported a grinding productivity of 7.29 m³/h with a two-man crew that was based on a single 1-hour observation. However, their productivity was over 3.4 times lower than other studies (Bolding et al. 2009; Yoshida & Sakai 2014a; Zamora-Cristales et al. 2015). Thus, further research on the efficacy and profitability of biomass operation systems is needed to utilize forest biomass and its potential for production expansion in Korea.

National Forestry Cooperative Federation (NFCF) is one of the companies that produce wood chips in Korea. It purchased and owns a mobile grinder system to promote forest biomass production in Korea, and allows rental of the system. However, the profitability of utilizing woody biomass material with the mobile grinder system has not been investigated; therefore, small-scale forestry owners and contractors do not rent the mobile grinder system for forest biomass production. Information about its efficacy and profitability could encourage forest owners to adopt this relatively new operation.

The objectives of this study are to assess the efficacy and profitability of utilizing forest biomass with a mobile grinder system in Korea by investigating production time and productivity of the mobile grinder system using time study. We identify potential problems and the areas of improvement for increasing the efficacy and profitability of the mobile grinder system.

Materials and methods

Mobile grinder system

The mobile grinder system consists of a mobile tub-grinder, Duratech 3010T (DuraTech Industries 2014), a loader, grapple excavator Daewoo Solar 200W, and a three-man crew to operate the two machines (Figure 1; Table 1). The grinder is an industrial tub grinder that has a compact stacking conveyor and a crawler-type track system. An operator can move the grinder to a different location and change its position without additional equipment. However, it needs a loader to feed woody material into the grinder tub. Therefore, a grapple excavator was included in the mobile grinder system. The distance between the grinder and loader during the operations was within 10 m.

Figure 1. Tub grinder (DuraTech 3010T) and grapple excavator loader (Daewoo Solar 200W).

Table 1. Specification of the grinder and loader used for mobile grinder system in Korea.

Grinder	Duratech 3010T	Loader	Daewoo Solar 200W
Weight	20.2 ton	Weight	19.2 ton
Transport length	11.07 m	Overall length	9.29 m
Transport width	2.59 m	Overall width	2.49 m
Transport height	3.45 m	Overall height	3.74 m
Ground clearance	0.338 m	Bucket capacity	0.750 m^3
Engine power	354.2 kW (475 HP)	Engine power	107.4 kW (144 HP)
Fuel capacity	605.6 liter	Fuel capacity	300 liter
Hammers	20 fixed single bolt or 40 swinging
Hammer rods	Eight 38.1 mm × 1.09 m long
Screens	Split screens 25.4 mm thick in various sizes
Screen area	1.57 m^2

Note: DuraTech Industries (2014)

Study site

The study was carried out over three days during January of 2014 at a loading site in Nonsan-si, Chungcheongnam-do, Republic of Korea (36°13′N, 127°18′E). Most of the woody material fed into the grinder was mixed hardwood slash such as brushes and shrubs less than 7 cm in diameter. They were transported and arranged to a loading site for efficient grinding operation.

Time study

A time study was carried out to measure time consumption and calculate the productivity of the mobile grinder system. First, we defined seven work elements and grouped them into productive and non-productive work time based on whether chips were produced (Table 2). All remaining time other than productive work time was considered delay, and non-productive work time was considered “organizational delays” (Spinelli & Visser 2009).

Table 2. Definition of work elements for the mobile grinder system.

Non-productive/productive work time	Work element	Definition
Non-productive work time	Preparation and positioning	Checking and starting up grinder and loader, and moving them to adequate position
Productive work time	Grabbing	Grabbing woody material with a grapple
	Grapple swing	Swinging a grapple with woody material to feed into grinder
	Feeding	Feeding woody material into grinder
	Helping in feeding	Pressing woody material into grinding tub and clearing debris around the grinding area for next feed-in
	Booming out	Booming out a grapple to grab woody material
Non-productive work time	Fueling and knife change	Fueling the loader/grinder and changing the knives of the grinder

The time study was carried out at two levels: cycle, and work element levels. At the cycle level where the mobile grinder system started and ended without a break, we measured productive and non-productive work time using a stopwatch for a total of five work cycles. At the work element level the grinding operations were recorded using a camcorder during the productive work time. We analyzed a part of the recorded grinding operations (39.65 minutes) using Windows Media Player to determine time consumed for each work element during the productive work time. The operation times for five work elements were compared using a two-tailed t-test with a significance level of 0.01.

Analysis of profitability

A number of factors are needed to determine the profitability of the mobile grinder system: amount and unit price of grinding production (wood chips), cost of the mobile grinder system, loading, and transportation costs. We calculated the amount of grinding production based on the time study results. This study did not measure a grinding production rate on site, and therefore used production capability (theoretical production rate under ideal condition) from the manufacturer (Shinyoung Equipment Solutions 2016) and estimated productivity from the interviews with grinder operators instead. For the unit price we used market sales price for sawdust and wood wastes (NFCF 2014) to calculate the values of grinding production, because no purchase price at a biomass plant was available. The mobile grinder system could be rented from NFCF in Korea for W4,000,000/day (Table 5). Loading and transportation costs were based on KOFPI (2014). In particular, the transportation cost varied depending on wood type, distance, and truck used; and we assumed hardwood, 100–200 km distance, and a 20-ton truck used for transportation in this study. Because the mobile grinder system could be rented on a daily basis, we calculated income and costs from the mobile grinder system and converted them to daily values.

Results and discussion

Productivity of the mobile grinder system

The time study at the cycle level showed that the total work time per cycle was 115.8, minutes of which productive and non-productive work time were, respectively, 79.1 and 36.7 minutes (Table 3). Considering 8 working hours a day, it is possible to have four work cycles a day, which might cause machine overload and breakdown more often (personal communication with grinder operators 2014), and thus increase delay time to repair the grinder. Therefore, the grinder systems could run three work cycles a day, resulting in a productive work time of 237.4 minutes a day (utilization rate, 49.4%) and a delay time of 242.6 minutes a day (50.6%). The utilization rate was very low compared to an average utilization rate of 73.8% from 63 chipping productivity studies (Spinelli & Visser 2009). Conversely, the delays are much higher than the average delay value of 26.2%. To increase profit from the mobile grinder system, an increase in work cycles per day should be considered: 3.5 work cycles a day would result in an average utilization rate of 57.7%; and four cycles, 65.9%. Also, non-productive work time (i.e. organizational delays) should be reduced. Spinelli and Visser (2009) reported that two-thirds of the total delay time were organizational delays that could be reduced by operation management such as good operational planning and layout.

Table 3. Work time and productivity per cycle and day (values in parentheses are standard deviation).

Measurement	Cycle	Day*
Productive work time (min)	79.1 (± 3.34)	237.4
Non-productive work time (min)	36.7 (± 2.79)	110.1
Total work time (min)	115.8	347.5
Production capability (m^3)	151.6^†	454.9
Estimated productivity (m^3)	82.1	246.2^‡

Note: The mobile grinder system consists of a three-man crew. *Day consists of three cycles. ^†Based on 115 m³/h for brushes and shrubs (Shinyoung Equipment Solutions 2016). ^‡Daily production was 160 tons (160 tons / (0.65 ton/ m³) = 246.2 m³) (personal communication with grinder operators 2014).

Considering that hourly production capability of the mobile grinder is 115 m³/h for brushes and shrubs (Shinyoung Equipment Solutions 2016), daily production capability is 332.3 m³/day. This is 35% higher than the estimated productivity (personal communication with grinder operators 2014; 160 GMT (Green Metric Ton) ≈ 246.2 m³/day = 62.2 m³/h, assuming 0.65 GMT/m³). The grinding productivity varies with grinding machine, type, feedstock species, moisture content, type, and grate size (Dukes et al. 2013; Han et al. 2015). The estimated productivity was lower than published grinding productivities of other grinder types, 70.8–83.9 m³/h (Han et al. 2015; Bisson et al. 2016) and 75.0–112.7 m³/h (Manzone & Balsari 2015), but was close to the tub-grinding productivity in Japan, 60 m³/h (Yoshida & Sakai 2014a) or higher than the tub-grinding productivities in USA, 24.7 m³/h (Bolding et al. 2009) and 29.2 m³/h (Zamora-Cristales et al. 2015). Also, it was much higher than the grinding productivity of 7.29 m³/h from the same mobile grinder system based on single 1-hour observation (Mun et al. 2014).

The work elements by operation time during productive work time are in decreasing order: helping in feeding (36.9%), grabbing (23.8%), grapple swing (16.3%), booming out (15.3%), and feeding (7.7%) (Table 4). Especially helping in feeding has much higher standard deviation, indicating that helping in feeding was conducted only when it is needed, while the other work elements were required every time. For the analyzed grinding operations recorded, five work elements during the productive work time were repeated 44 times. Among those, no helping in feeding was needed 16 times.

Table 4. Work time by work element and cycle.

		Work time by element
Non-productive/productive work time	Work element	Mean (s)	SD* (s)	Percent (%)	Work time per cycle (min)
Non-productive work time	Preparation and positioning	NA^†	NA	NA	11.4
	Grabbing	12.9^a	8.0	23.8	18.9
	Grapple swing	8.8^b	4.1	16.3	12.9
Productive work time	Feeding	4.1^c	1.6	7.7	6.1
	Helping in feeding	19.9^a	25.5	36.9	29.2
	Booming out	8.3^b	5.6	15.3	12.1
	Total	54.1	NA	100.0	79.1
Non-productive work time	Fueling and knife change	NA	NA	NA	25.3

Note: Grinding production times per cycle were calculated by multiplying percent and the total productive work time from Table 2 (79.1 min). *Standard deviation. ^†Not available. Superscript letters (a, b, and c) next to means represent significant difference at α = 0.01.

Table 5. Itemized daily rental cost of the mobile grinder system.

		Daily cost
Item	Detail	W/day	US$/day*
Fuel	7 0 liter/h × 8 h/day × W1750/liter	980,000	930
Loader rental	Grapple excavator	650,000	617
Knife (supplies)	2 0 units/set^† × W30,000/unit	600,000	570
Labor	W200,000 (grapple excavator operator) + W150,000 (senior worker) + W80,000 (junior worker)	430,000	408
Maintenance	Machine oils, compressor, trailer costs	1,000,000	949
Other fees	Insurance, management fee	340,000	323
Total		4,000,000	3798

Note: Based on NFCF in Daejeon, Korea (computer printout, 2014). *Converted from Korea Won based on 2014 currency exchange rate (KEB Hana Bank 2016). ^†A set of grinder knives that consists of 20 individual knives was needed daily.

Profitability of mobile grinder system

There is a profitability of the mobile grinder system based on the study analysis. Use of the grinding production capability results in W5,522,000/day profit (Table 6), while use of the estimated productivity results in W1,152,000/day (Table 7). The current market price of final products was used to calculate the values of grinding production from the system. Because the purchase price at a biomass plant was not available, break-even points were calculated as percent of the sales price: 70.6% for the production capability and 88.7% for the estimated production; i.e. the mobile grinder system can generate profit if the purchase price is over 88.7% of the sales price. Considering that purchase price can be much lower than market sales price due to transaction costs, such as sales margins, the profitability of the mobile grinder system seems to be marginal or none. For example, an interview with a chipping factory worker revealed that the purchase price was 47–79% of the sales price, indicating no profitability of the mobile grinder system with the estimated production.

Table 6. Profitability of the mobile grinder system using the production capability.

	Unit price	Daily production/cost
Item	W/m^3	W/day	US$/day*
Grinding production for sawdust and wood wastes	41,330^†	+18,802,670	+17,853
Rental cost of the mobile grinder system		–4,000,000^‡	–3798
Loading cost (hardwood)	4600^§	–2,092,724	–1987
Transportation cost (hardwood, 100–200 km distance, 25 ton truck)	15,800^§	–7,188,052	–6825
Total		+5,521,894	+5243

Note: Based on the production capability from the manufacturer (Shinyoung Equipment Solutions 2016). *Converted from Korea Won based on 2014 currency exchange rate (KEB Hana Bank 2016). ^†Market sales price from NFCF (2014). ^‡Table 5. ^§KOFPI (2014).

Table 7. Profitability of the mobile grinder system using the estimated productivity.

	Unit price	Daily production/cost
Item	W/m^3	W/day	US$/day*
Grinding production for saw dust and wood wastes	41,330^†	+10,173,538	+9660
Rental cost of the mobile grinder system		–4,000,000^‡	–3798
Loading cost (hardwood)	4,600^§	–1,132,308	–1075
Transportation cost (hardwood, 100–200 km distance, 25 ton truck)	15,800^§	–3,889,231	–3693
Total		+1,152,000	+1094

Note: Based on the estimated productivity from the interviews with grinder operators. *Converted from Korea Won based on 2014 currency exchange rate (KEB Hana Bank 2016). ^†Market sales price from NFCF (2014). ^‡Table 5. ^§KOFPI (2014).

An increase in work cycles per day could increase profit: 3.5 work cycles a day would result in W2,011,000/day profit using the estimated productivity; and four work cycles, W2,869,000/day profit. However, the increase in work cycles might cause machine overload and more frequent breakdown (mechanical delays) (personal communication with grinder operators 2014), and thus decrease the productivity and profit. Also, a decrease in organizational delays and an increase in productivity of the mobile grinder system would increase profit. For example, better operational planning, such as using the optimized number of work cycles per day, could decrease organizational delays. Training operators and workers or paying incentives for the crew based on biomass production amount can increase the productivity and profit.

Conclusions

A mobile grinder system used in Korea consists of a mobile tub grinder, a grapple excavator (loader), and a three-man crew to operate the two machines. This study found that operating three work cycles a day was inefficient for the mobile grinder system, resulting in a utilization rate of 49.4% and delays of 50.6%. Increasing work cycles per day and decreasing organizational delays by better operation management are recommended to increase profit. There was a difference between the production capacity, 332.3 m³/day, and the estimated productivity, 246.2 m³/day, that was based on the interviews with grinder operators. The on-site productivity should be measured and studied to more accurately assess and increase the efficacy of the mobile grinder system in the future. This study found the mobile grinder system could be profitable based on available market sales price. Considering transaction costs between purchase and sales prices, such as sales margins, the profitability may be marginal or none. The scale of production and purchase price of wood chips at biomass plants should be investigated to further assess the profitability of the mobile grinder system in the future. The study results can be used as a justification for the mobile grinder system; encourage forest managers to adapt this biomass operation; and help to promote forest biomass production in Korea.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by Chungnam National University.