Plant Performance Report
Semirara Coal: Effect on Boiler Operation
and Economical Price Determination
PPR-TSD-23-004
Prepared by:
RB Del Rosario
Date Created:
Reviewed by:
PC Licot, VH Panes
Revision:
Approved by:
JV Diamante
Date Approved:
January 18, 2023
February 9, 2023
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Date:
February 9, 2023
To:
Joel D. Ysip
Plant Manager
Revision:
0
Page:
2 of 17
Reynaldo E. Francisco
Operations Manager
Gary A. Algodon
Supply Chain Manager
Cc:
Christian A. Sabigan
Water Treatment Supervisor
All Managers
Subj:
Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Executive Summary







Hardgrove Grindability Indices from COA suggest that Semirara coals (42.92 HGI) are harder and more erosive than
Indonesian coals (51.78 HGI), as indicated by the former’s lower HGI and by the PSD measured at crusher upstream.
The ash and silica content of Semirara coals (8.11% ash, 51.04% SiO2) is also higher than that of Indonesian coals
(4.97% ash, 36.61% SiO2), increasing concentrations of erosive ash in the bed material.
The 15.85% increase in average and 28.95% increase in maximum freeboard dP following the start of Semirara
coal firing have accelerated boiler tube erosion due to the higher flue gas velocities and bed material concentrations in
the upper furnace.
Data show severe slagging and fouling potential of the Semirara coal sample. Although slagging should not be of
concern, the decrease in finishing superheater and reheater desuperheater spray water quantities and the frequent
localized overheating in the backpass indicate increased fouling rates.
The higher total sulfur content of Semirara coals (0.57% S) than Indonesian coals (0.2% S) subjects the air preheaters
to greater corrosion of cold end heating elements.
Central composite design was used to analyze the effect of unit costs and average WESM price on the contribution
margin difference between pure Indonesian coal firing and 2 Indo 1 Semirara coal firing, at fixed consumption rates,
service and outage days, net load factor, and additional APMS and forced outage costs.
Latest data suggest that 2 Indo 1 Semirara coal firing would match the contribution margin from pure Indonesian coal
firing at Semirara coal prices of ~PHP 8,613.15/MT and ~PHP 9,392.49/MT in years 1 and 2, respectively.
Findings and Analysis
Effect of Semirara Coal on Boiler Tube Erosion
In 2022, the plant has been troubled by three forced outages due to boiler tube leakage, two of which led to earlier than
scheduled annual preventive maintenance shutdown. Following thorough research, it was determined that the use of Semirara
coal since January 21 last year has significantly increased the rate of boiler tube erosion. Aside from the observed upswing in
furnace freeboard differential pressure, two coal properties were analyzed: Hardgrove Grindability Index and ash content.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
3 of 17
Figure 1.1 Unit 3 boiler tube leakage at evaporator panel #6 ruptured tube. Photos by TSD Reliability.
Recent literature on coal abrasiveness concludes that the abrasion index of coals increases for every increase in ash
content and for every decrease in grindability (Alekhnovich et al., 2021). Presented in Figure 1.2 are the weighted average values
of these properties for each coal mixture, showing decreasing coal quality and desirability as the percentage of Semirara coal
increases.
60.00
51.78
48.83
50.00
45.87
42.92
40.00
30.00
20.00
10.00
4.97
6.02
7.06
8.11
Pure Indonesian
2 Indo, 1 Semirara
Hardgrove Grindability Index
1 Indo, 2 Semirara
Pure Semirara
Ash Content (ADB), %
Figure 1.2 Weighted average HGI and ash content per coal mixture
The Hardgrove Grindability Indices (HGI) from the certificates of analysis (COA) suggest that Semirara coals (42.92
HGI) are harder and more erosive than Indonesian coals (51.78 HGI), as indicated by the former’s lower HGI and by the
particle size distribution measured at the crusher upstream. In addition, the acceptable HGI range based on the coal supply
evaluation criteria set by SCPC is 46-56 HGI. Although erosive metal loss decreases as furnace temperatures increase due to the
softening of particles, the initial deformation temperatures of both Indonesian coals (1,212.15oC) and Semirara coals (1,093.51oC)
are sufficiently high to resist the softening process.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
4 of 17
Table 1.1 PSD of Indonesian and Semirara coals last August 14, 2022
Mean Diameter
Standard, mm
D – 99
D – 50
D – 05
6.0 – 9.0
0.7 – 1.5
< 0.1
Indonesian: MV SL Rose (2)
Sample Results, mm
0.9652
0.0406
Semirara: Barge Karangalan 2 (6)
Sample Results, mm
1.3209
0.1046
The ash content of Semirara coals (8.11% ash) is also higher than that of Indonesian coals (4.97% ash). Coal
abrasiveness increases proportionally with ash content due to the increase in the quantity of abrasive material such as aluminum,
silicon, and iron oxide compounds, which have high particle hardness and thus provide greater kinetic energy upon impact, as
stated in the aforementioned literature. These compounds are present in both Indonesian and Semirara coal ash in the form of
alumina (Al2O3), silica (SiO2), and hematite (Fe2O3) as shown in Figure 1.3.
Since no ash analyses are provided in the COA of Semirara coals, an independent coal analysis was conducted for Barge
Karangalan 2 (8) samples in Masinloc Power Plant last September 9, 2022 to determine the composition of Semirara coal ash.
Another study on the development of a predictive model for abrasion has clearly identified that both quartz, expressed as the
combination of SiO2 and Al2O3 in this study, and ash content are the key predictors for abrasion (Bandopadhyay, 2010).
60.00
51.04
50.00
40.00
36.61
30.00
20.00
14.81
11.19
12.61
10.00
8.74
SiO2, %
Al2O3, %
Indonesian Coal
Fe2O3, %
Semirara Coal
Figure 1.3 Weighted average percentages of alumina, silica, and hematite in coal ash
Aside from the large quantity of erosive particles, another factor that accelerates erosion is high flue gas velocity, which
increases the kinetic energy of the entrained particles as they strike the tube surfaces. Erosion must have been minimal on vertical
tubes in a CFB boiler, where bed material flows parallel to the surfaces. However, any region inside the furnace where channeling
or eddying of flue gas occurs is susceptible to erosion.
Presented in Figure 1.4 are trends from January 1, 2021 to September 28, 2022, the date when the last boiler tube leakage
occurred in Unit 3. The figure shows drastic increase in furnace freeboard differential pressures (dP) following the use of
Semirara coal on January 21, 2022, which has escalated flue gas velocities and bed material concentrations in the upper furnace.
At 150 ±1 MW, a 15.85% increase in average freeboard dP was observed, while the maximum freeboard dP surged by 28.95%.
Unit 4 suffered the highest increase in average and maximum freeboard dP, yielding percent increase of 30.22% and 39.38%,
respectively.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
5 of 17
Figure 1.4 Comparison among unit furnace freeboard dP
The correlation between freeboard dP and coal mixture presented in Figure 1.5 is worth noting as it shows the general
effect of Semirara coals on freeboard dP. The following data are the average freeboard dP observed at 150 ±1 MW from January
21, 2022 to September 28, 2022.
140.00
120.00
100.00
80.00
60.00
40.00
20.00
-
124.86
117.81
105.27
108.26
93.70
79.06
77.12
58.20
57.26
77.97
67.26
Unit 1
Unit 2
Pure Indonesian
83.53
2 Indo, 1 Semirara
85.83
Unit 3
1 Indo, 2 Semirara
Unit 4
Pure Semirara
Figure 1.5 Furnace freeboard dP in mmH2O vs coal mixtures
Although it was Unit 4 which has experienced the greatest increase in freeboard dP, it was Unit 1 which encountered
boiler tube leakages last May 29, 2022 and August 6, 2022, as well as Unit 3 last September 28, 2022. Summarized in Figure 1.6
are the number of days each unit was using each coal mixture from January 21, 2022 to September 28, 2022, and in Figure 1.7
are the actual consumptions and average coal mixtures during the said period, where it is evident that Units 1 and 3 have been
the top Semirara coal consumers at 46.10% and 32.78%, respectively. This implies that the compounded effect of high freeboard
dP and increased particle erosivity speeds up the rate of boiler tube erosion.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
6 of 17
200
154
140
150
118
111
100
50
81
46
23
28
48
57
63
41
6
0
Unit 1
Unit 2
Pure Indonesian
2 Indo, 1 Semirara
Unit 3
1 Indo, 2 Semirara
Unit 4
Pure Semirara
Figure 1.6 Number of operating days per coal mixture
100%
219,918.55
326,133.43
302,930.12
315,556.72
137,959.69
147,747.63
138,517.57
Unit 2
Unit 3
Unit 4
80%
60%
40%
188,099.80
20%
0%
Unit 1
Semirara Coal Consumption, MT
Indonesian Coal Consumption, MT
Figure 1.7 Average coal mixture per unit
Comparative analysis on boiler tube erosion rates for Unit 1, which has the highest Semirara coal consumption, was
conducted based on historical UTG data of tubes 3-7 and 169-172 recorded by TSD Reliability. During the 2021 APMS, it was
observed that even after 18 months and 15 days of operation since the 2020 APMS, the thickness wastage was only 2.39 mm,
yielding a 0.1292 mm/month erosion rate for pure Indonesian coal consumption. In addition, ceramic coating was applied
on the furnace roof area during the 2021 APMS.
Meanwhile, the unit experienced forced outage due to boiler tube leakage from the furnace roof last May 29, 2022,
where tubes 3-7 and 169-172 were replaced. During the emergency shutdown, it was observed that after 9 months and 7 days
of operation since the 2021 APMS, the thickness wastage was already 5.5 mm, yielding a 0.5957 mm/month erosion rate
for 25.18% or 133,222.99 MT of Semirara coal consumption.
The unit encountered yet another forced outage due to boiler tube leakage from the furnace roof side wall last August
6, 2022, days prior to its scheduled planned outage. During the 2022 APMS, it was observed that even after 1 month and 28
days of operation since the emergency shutdown, the thickness wastage was already 1.2 mm, yielding a 0.6207 mm/month
erosion rate for 35.48% or 39,060.81 MT of Semirara coal consumption.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
7 of 17
Effect on Backpass Fouling and Air Preheater Corrosion
As of January 18, 2023, the plant has 63 Semirara coal deliveries in total, all without ash and ultimate analyses provided
in their COA. Being one of the only few references cited in ASME PTC 4-2008 due to their extensive use in the industry, the
following analysis is based on formulas provided by The Babcock & Wilcox Company. Calculations were made using data
provided in the COA of Indonesian coals and data gathered from the independent coal analysis for Barge Karangalan 2 (8)
samples, and the resulting slagging and fouling indices presented in Table 1.2 show severe high temperature ash deposition
potential of the Semirara coal representative.
Table 1.2 Summary of calculated ash deposition indices
Particulars
Weighted Avg. Slagging Index
Bituminous Ash
Lignitic Ash
Weighted Avg. Fouling Index
Bituminous Ash
Lignitic Ash A
Lignitic Ash B
Shipment year
2016
2017
2018
2019
2020
2021
2022
Indonesian
Semirara
0.14
0.18
0.31
0.16
0.15
2245.46
2211.42
2215.47
2143.72
2229.02
2244.12
0.34
0.42
0.42
0.20
0.33
0.68
0.83
0.98
1.38
1.32
1.37
2.00
1.02
-
2285.02
1922.00
-
1.21
-
4.36
Fe2O3 > CaO + MgO
Fe2O3 < CaO + MgO
Fe2O3 > CaO + MgO
Fe2O3 < CaO + MgO
Fe2O3 < CaO + MgO
CaO + MgO + Fe2O3
> 20%
CaO + MgO + Fe2O3
< 20%
Na2O
Na2O
<3
< 1.2
3-6
>6
1.2 - 3.0
> 3.0
Ash classification
Ash deposition index formula
S*(B/A)
[(Max HT) + 4*(Min
IDT)]/5
Na2O*(B/A)
B = basic ash constituents (CaO + MgO + Fe2O3 + Na2O + K2O), %
A = acidic ash constituents (SiO2 + Al2O3 + TiO2), %
S = total sulfur on dry basis, %
CaO = calcium oxide from ash analysis, %
MgO = magnesium oxide from ash analysis, %
Fe2O3 = ferric oxide from ash analysis, %
Na2O = sodium oxide from ash analysis, %
K2O = potassium oxide from ash analysis, %
SiO2 = silicon dioxide from ash analysis, %
Al2O3 = aluminum oxide from ash analysis, %
TiO2 = titanium dioxide from ash analysis, %
Max HT = higher of the reducing or oxidizing hemispherical temperatures, oF
Min IDT = lower of the reducing or oxidizing initial deformation temperatures, oF
Ash deposition potential classification
Low
Medium
High
Severe
< 0.6
0.6 - 2.0
2.0 - 2.6
> 2.6
> 2450
2250 - 2450
2100 - 2250
< 2100
< 0.2
0.2 - 0.5
0.5 - 1.0
> 1.0
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
8 of 17
Coal records were classified into two categories based on the chemical composition of their ash. Under bituminous ash
are those with more Fe2O3 than the sum of CaO and MgO, while those with less Fe2O3 than the sum of CaO and MgO are
categorized as lignitic ash. For the fouling index calculations, coals with lignitic ash were further classified into two subcategories,
depending on whether the sum of the three compounds is greater or less than 20% by weight of ash. Weighted average total
sulfur content, ash analysis, and ash fusion temperature data were then used in the provided formulas to determine the slagging
and fouling indices.
The initial deformation (IDT) and hemispherical (HT) temperatures of coal ash indicate the deposit surface temperature
range where plastic slag, which is too viscous to flow and will continue to build in thickness, is likely to exist. Slagging therefore
should not be of concern in the plant if furnace temperatures are maintained between the normal operating range of 850 oC to
950oC, which is well below the lowest recorded IDT and HT of 1023oC and 1041oC, respectively.
Fouling on the other hand must be monitored as higher rates of ash deposition on convection heat absorbing surfaces
are evident since Semirara coals were first utilized. Fouling occurs when volatile forms of sodium and potassium in the coal
vaporize during combustion. As heat is absorbed and flue gas temperatures are lowered in the backpass, compounds formed
from subsequent reactions between these alkali metals and sulfur in the flue gas condense on fly ash and form a layer of bonded
deposits on tube surfaces. Presented in Figure 1.8 is an ash deposit sample dislodged from a finishing superheater upper tube
last Unit 1 2022 APMS.
Figure 1.8 Increased ash deposition on backpass tubes. Photos by TSD Reliability.
Even without the calculated ash deposition indices, the observed increase in fouling may be directly associated with the
increase in alkali content of coal ash. As presented in Table 1.3, the Semirara coal ash representative is beyond the 3% maximum
acceptable alkali content and 1,170oC minimum acceptable IDT stated in the coal supply evaluation criteria, where it can
also be noted that Na2O makes up the larger fraction of the alkali content.
Table 1.3 Acceptable IDT and alkali content vs actual data
Particulars
IDT (Reducing)
Alkali content (Na2O + K2O)
Na2O content on dry basis
K2O content on dry basis
Acceptable Range
> 1,170oC
< 3%
-
Indonesian Coal
1,212.15oC
1.92%
1.21%
0.72%
Semirara Coal
1,093.51oC
5.22%
4.36%
0.86%
The requirements of the main and hot reheat steam temperature control system were used as an indication of fouling
in the finishing superheaters and reheaters since the spray water flow rates of their respective desuperheaters reflect the changes
in tube surface cleanliness. As presented in Figure 1.9, a decrease in spray water quantities was observed following the
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
9 of 17
start of Semirara coal consumption, which indicates somewhat lower steam temperatures due to the negative effect of tube
fouling on efficient heat transfer. The notable downward trends can be especially observed in all units during the first few weeks
of Semirara coal firing, where the plant was mainly in 1 Indo 2 Semirara operation.
Figure 1.9 Low desuperheater spray water flow rates during high Semirara coal consumption
Ash accumulations also result in unequal flue gas distribution and frequent localized overheating in the backpass,
especially around the economizer #3 upper, which is being addressed directly with sootblowers. The sootblowing frequency was
also increased to repress the higher fouling potential of Semirara coals, from once per shift when the plant was still in pure
Indonesian coal firing to twice per shift or as necessary when mixed coal firing began.
Certainly, variations in coal properties greatly affect sootblowing requirements in addition to unit load changes, furnace
temperature fluctuations, and air flow conditions. Sootblower operation must therefore be continually assessed and reviewed
based on changing operating parameters, as sootblowers are most effective in removing dry and loosely bonded deposits that
occur in the early stages of fouling.
In addition to increased fouling, Semirara coals also resulted in an increase in flue gas corrosivity. Due to the higher
total sulfur percentage (ADB) of Semirara coals (0.57% S) than Indonesian coals (0.2% S), the air preheaters are subjected to
greater corrosion of cold end heating elements as presented in Figure 1.10, and other structures along the flue gas path. About
0.25% to 1.5% of the sulfur dioxide (SO2) produced from coal combustion is converted to sulfur trioxide (SO3) as it reacts with
oxygen in combustion air. SO3 then combines with moisture in the flue gas, forming sulfuric acid (H 2SO4) vapor.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
10 of 17
Figure 1.10 Corroded air preheater cold end heating elements. Photos by TSD Reliability.
The H2SO4 vapor in the flue gas condenses on surfaces at temperatures below its acid dew point, which ranges from
121oC to 149oC. Summarized in Figure 1.11 are the average flue gas outlet and air inlet temperatures from January 21, 2022 to
September 28, 2022, estimated to be equal to the cold end metal temperature of each unit at 150 ±1 MW.
160.00
141.42
140.00
136.82
120.00
136.70
135.43
100.00
84.94
80.00
60.00
82.52
59.48
57.83
58.13
57.68
40.00
53.93
52.90
82.53
82.04
52.77
52.99
20.00
Primary Air Inlet, °C
Secondary Air Inlet, °C
Unit 1
Unit 2
Flue Gas Outlet, °C
Unit 3
Cold End Metal, °C
Unit 4
Figure 1.11 Estimated cold end metal temperatures
The air preheaters may be designed to operate with flue gas outlet and cold end metal temperatures below the acid dew
point as the thermal efficiency gained offsets the additional maintenance costs, but these costs are most likely to escalate due to
the effect of firing high-sulfur Semirara coals.
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
11 of 17
Figure 1.12 Significant increase in SO2 levels due to Semirara coal consumption
Although SO2 is captured in the furnace by limestone, trends presented in Figure 1.12 show a significant increase in
SO2 levels in 2022 due to the use of Semirara coals despite regular limestone injection. In addition, furnace temperatures above
899oC, as presented in Figure 1.13, lead to the dissociation of calcium sulfate (CaSO4) produced during the sulfation process,
which reduces sulfur capture efficiency and promotes flue gas conditions ideal for greater cold end corrosion.
Figure 1.13 Historical furnace temperature data
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
12 of 17
Although the amount of SO3 generated increases with increased oxygen in the flue gas, operational and design
constraints highlight the evident disadvantage of using high-sulfur coals. First, excess air is supplied into the furnace in addition
to the stoichiometric air quantity to ensure complete coal combustion. Second, the plant’s regenerative-type air preheaters have
about 8% air ingress from the air side to the flue gas side by design, providing more oxygen and moisture for SO 3 and H2SO4
formation.
At what price are Semirara coals economical?
Due to the occurrence of boiler tube leakages in the units with the highest Semirara coal consumptions, along with the
crucial findings in this report, it can be inferred that Semirara coals are detrimental to boiler operation. However, due to the
significant difference between Indonesian and Semirara coal prices, a sensitivity analysis was conducted to determine the
Semirara coal price where the projected decrease in operational cost can counter the projected outage costs.
Table 1.4 General assumptions used in the sensitivity analysis
Service days
Planned outage days
APMS extension days
Forced outage days
Case 1:
Pure Indo
344
21
0
0
Year 1
Case 2:
2 Indo 1 Semirara
323.49
21
9
11.51
Case 1:
Pure Indo
344
21
0
0
Year 2
Case 2:
2 Indo 1 Semirara
344
21
0
0
Presented in Table 1.4 are the two-year pure Indonesian coal firing and 2 Indo 1 Semirara coal firing operations
investigated in this study. Case 1 assumes pure Indonesian coal firing for 344 days, with 21 days for APMS each year.
Operational costs for both years are limited to the cost of Indonesian coals, silica sand, limestone, and demineralized water
consumed, which are based on unit costs summarized in Table 1.5.
Table 1.5 Latest unit costs from Finance and WTP
Indonesian Coal, PHP/MT
Semirara Coal, PHP/MT
Silica Sand, PHP/MT
Limestone, PHP/MT
Demineralized Water, PHP/m3
Diesel Oil, PHP/L
Unit Cost
7,933.92
6,968.47
7,062.14
1,964.29
86.25
58.20
Remarks
Weighted average Indonesian coal price for December 2022
Weighted average Semirara coal price for December 2022
Gross delivered silica sand price as of December 31, 2022
Gross delivered limestone price as of December 31, 2022
Latest estimated demineralized water production cost
Gross delivered diesel oil price as of December 31, 2022
Meanwhile, case 2 assumes 2 Indo 1 Semirara coal firing for 232.49 days in year 1, with 11.51 days of forced outage,
21 days for APMS, and 9 days of APMS extension due to the extent of boiler tube damage. The duration of forced outage was
based on the actual Unit 1 emergency shutdown due to boiler tube leakage. Its anticipated occurrence was based on the projected
218.32 days of using 2 Indo 1 Semirara coal mixture prior to boiler tube leakage, estimated using the 133,222.99 MT of Semirara
coal consumed by Unit 1 at 648.58 MT/day prior to tripping last May 29, 2022, and 147,747.63 MT for Unit 3 at 638.96 MT/day
prior to tripping last September 28, 2022. Following the application of additional ceramic coating and thermal spray during the
APMS, it was assumed that each unit would be capable of operating for 344 days in year 2, with 21 days for APMS.
For the operational costs, included in both years are the costs of Indonesian and Semirara coals, lower silica sand
consumption due to the higher ash content of Semirara coals, higher limestone consumption due to the higher sulfur content
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
13 of 17
of Semirara coals, and demineralized water consumed. On the other hand, outage costs in year 1 include the forced outage cost,
start-up cost after the forced outage, and additional APMS cost.
Presented in Table 1.6 are the differences in contribution margin between the two cases each year for one unit. Annual
revenues were calculated using the corresponding service days, average forecasted net load factor of 94.9375% for 2023, net
capacity of 134 MW, and average WESM price of PHP 7.38/kWh as of January 17, 2023. It was observed that the contribution
margin difference changes by PHP 206,699.42 in year 1 and by PHP 219,802.66 in year 2 for every change in Semirara
coal price by PHP 1.00.
Table 1.6 Contribution margin differences in years 1 and 2
Year 1
Case 1: Pure Indo
Case 2: 2 Indo 1 Semirara
Year 2
Case 1: Pure Indo
Case 2: 2 Indo 1 Semirara
Revenue,
PHP
7,751,194,516.80
7,289,117,796.19
Operational
Cost, PHP
5,612,883,920.52
4,777,236,316.15
Outage Cost,
PHP
0
33,616,483.81
Contribution
Margin, PHP
2,138,310,596.28
2,478,264,996.23
339,954,399.96
Revenue,
PHP
7,751,194,516.80
7,751,194,516.80
Operational
Cost, PHP
5,612,883,920.52
5,080,078,134.90
Outage Cost,
PHP
0
0
Contribution
Margin, PHP
2,138,310,596.28
2,671,116,381.90
532,805,785.62
It is worth noting that 2 Indo 1 Semirara coal firing would still be more profitable by PHP 339.95M in year 1 despite
the additional outage costs, and by PHP 140.40M even at equal coal prices. Moreover, 2 Indo 1 Semirara coal firing would still
be more profitable by PHP 320.60M even at equal coal prices in year 2 due to the lower coal consumption as an effect of the
Semirara coals’ higher gross calorific values. Although recent data show higher profitability from 2 Indo 1 Semirara coal firing,
abrupt changes in prices highlight the need to determine the Semirara coal price that would match the contribution margins
from the two cases, which could serve as a basis of a Semirara coal’s preferability for procurement.
Figure 1.14 3D surface plots of the contribution margin difference regression models
A central composite design was used to analyze the effect of the unit costs and the average WESM price on the
contribution margin difference in both years, at fixed consumption rates, service days, outage days, net load factor, additional
APMS cost, and forced outage cost. An experimental design space was created based on reasonable fluctuations in unit costs
and average WESM price to develop regression models for contribution margin difference prediction, as presented in Figure
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
14 of 17
1.14. The ANOVA shows that all of the factors considered provide significant effect on the contribution margin difference in
year 1 as indicated by their less than 0.05 p-values, thus their inclusion in the final regression model. Meanwhile, only the unit
costs of coals, silica sand, and limestone affect year 2 contribution margin difference significantly.
Table 1.7 Final regression equations in terms of actual unit costs and average WESM price
Year 1 Contribution Margin Difference =
Year 2 Contribution Margin Difference =
Numerical Coefficient
- 23027623.107973
+ 286972.86024781
- 206699.44180238
+ 898.01555844378
- 4041.668325282
+ 1276.4608072227
- 124771.72047038
- 62969047.046626
206.99760523433
+ 260571.53833224
- 219802.67361862
+ 889.58732464283
- 4654.8923220849
*
*
*
*
*
*
*
*
*
*
*
*
*
*
Factor, Unit
Indonesian Coal, PHP/MT
Semirara Coal, PHP/MT
Silica Sand, PHP/MT
Limestone, PHP/MT
Demineralized Water, PHP/m3
Diesel Oil, PHP/L
Average WESM Price, PHP/kWh
Indonesian Coal, PHP/MT
Semirara Coal, PHP/MT
Silica Sand, PHP/MT
Limestone, PHP/MT
The regression equations presented in Table 1.7 were used to calculate the Semirara coal prices that would yield no
difference in contribution margin between the two cases. The latest available data suggest that 2 Indo 1 Semirara coal firing
would match the contribution margin from pure Indonesian coal firing in year 1 at a Semirara coal price of ~PHP
8,613.15/MT and in year 2 at ~PHP 9,392.49/MT. Using the suggested Semirara coal prices in the calculations results in
contribution margin differences of only PHP 28.74 and PHP 45.28 for years 1 and 2, respectively, proving the predictive power
of the generated regression equations. Still, use the equations with caution, as these do not consider the effect of the other factors
held constant on the contribution margin difference.
Recommendations
Item
Action
Responsible Group
01
Continue monitoring coal properties and assess other possible effects of varying coal quality
on boiler operation. Finalize the feasibility study on coal blending strategies to evaluate the
advantage of homogenized coal characteristics.
TSD Performance
02
As the plant fully shifts to 2 Indo 1 Semirara coal firing after the Unit 4 2023 APMS, ensure
that HGI, ash content, and other coal properties are within specifications. Acquire a third
party to randomly conduct ash and ultimate analyses for Semirara coal deliveries.
Procurement,
Water Treatment
03
Continue the implementation of the boiler tube leak reduction program by applying
additional thermal spray on the remaining critical areas such as the superheater panels.
TSD Reliability
04
Maintain furnace freeboard dP around 75-100 mmH2O and ensure normal air flow rates and
distribution to prevent high erosion rates in the upper furnace.
Operations
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
15 of 17
References













Alekhnovich, A.N., Artemieva, N.V., & Bogomolov, V.V. (2021). Definition and assessment of coal abrasivity. Power
Technology and Engineering, 55(9). https://doi.org/10.1007/s10749-021-01326-y
ASME PTC 4-2008. Fired Steam Generators Performance Test Codes.
Bandopadhyay, A.K. (2010). A study on the abundance of quartz in thermal coals of India and its relation to abrasion
index: Development of predictive model for abrasion. International Journal of Coal Geology, 84(1).
https://doi.org/10.1016/j.coal.2010.08.005
Basu, P. (2006). Material issues. Combustion and gasification in fluidized beds. Taylor & Francis Group.
Flynn D.J. (Ed.). (2011). Erosion. The NALCO guide to boiler failure analysis (2nd ed.). The McGraw-Hill Companies.
Formosa Heavy Industries Corp. (2015). Circulating Fluidized Bed Steam Generator Instruction Manual.
Indonesian and Semirara coals’ certificates of analysis (COA)
PIR-TSD-22-014. Unit 1 Backpass Area: Dry Ice and Manual Scraping Cleaning Inspection.
Tomei, G.L. (Ed.). (2015). Economizers and air heaters. Steam: Its generation and use (42nd ed.). The Babcock & Wilcox
Company.
Tomei, G.L. (Ed.). (2015). Fluidized bed combustion. Steam: Its generation and use (42nd ed.). The Babcock & Wilcox
Company.
Tomei, G.L. (Ed.). (2015). Fuel ash effects on boiler design and operation. Steam: Its generation and use (42nd ed.). The
Babcock & Wilcox Company.
Units 1-4 Distributed Control System (DCS)
Unit 1 Ultrasonic Thickness Gauging (UTG) data
Appendices
Appendix A Pure Indonesian coal firing
1. Total Projected Operational Cost, PHP
5,612,883,920.52
1.1 Projected Cost of Coal Consumed
MT/day
Days
PHP/MT
PHP
Indonesian Coal
2,044.90
344
7,933.92
5,581,084,244.72
MT/day based on the average daily feeder-based coal consumption of Unit 3 when in pure Indonesian coal firing and at
least 95% net capacity factor
1.2 Projected Cost of Silica Sand Consumed
MT/day
Days
PHP/MT
PHP
Silica Sand
5.74
344
7,062.14
13,937,176.24
MT/day based on the average daily formula-based silica sand consumption of Unit 3 when in pure Indonesian coal firing
1.3 Projected Cost of Limestone Consumed
MT/day
Days
PHP/MT
PHP
Limestone
18.04
344
1,964.29
12,190,411.50
MT/day based on the average daily formula-based limestone consumption of Unit 3 when in pure Indonesian coal firing
1.4 Projected Cost of Demineralized Water Consumed
m3/day
Demineralized Water
191.17
Days
344
PHP/m3
86.25
PHP
5,672,088.08
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Revision:
0
Page:
16 of 17
m3/day based on the average daily demineralized water consumption of Unit 3
Appendix B Year 1 of 2 Indo 1 Semirara coal firing
1. Total Projected Operational Cost, PHP
1.1 Projected Cost of Coal Consumed
MT/day
Indonesian Coal
1,287.42
Semirara Coal
638.96
4,777,236,316.15
Days
323.49
323.49
PHP/MT
7,933.92
6,968.47
PHP
3,304,263,165.68
1,440,378,564.86
4,744,641,730.54
MT/day based on the average daily feeder-based coal consumption of Unit 3 when in 2 Indo 1 Semirara coal firing and at
least 95% net capacity factor
1.2 Projected Cost of Silica Sand Consumed
MT/day
Days
PHP/MT
PHP
Silica Sand
3.15
323.49
7,062.14
7,198,457.04
MT/day based on the average daily formula-based silica sand consumption of Unit 3 when in 2 Indo 1 Semirara coal firing
1.3 Projected Cost of Limestone Consumed
MT/day
Days
PHP/MT
PHP
Limestone
31.57
323.49
1,964.29
20,062,174.16
MT/day based on the average daily formula-based limestone consumption of Unit 3 when in 2 Indo 1 Semirara coal firing
1.4 Projected Cost of Demineralized Water Consumed
m3/day
Days
Demineralized Water
191.17
323.49
m3/day based on the average daily demineralized water consumption of Unit 3
PHP/m3
86.25
2. Total Projected Outage Cost, PHP
PHP
5,333,954.40
33,616,483.81
2.1 Projected Additional APMS Cost
PHP
15,565,222.00
1,260,220.00
2,556,170.00
19,381,612.00
Additional Thermal Coating
Additional Consumables
Additional Fitters and Welders
All figures are based on the actual Unit 3 2022 additional APMS cost from TSD Planning
2.2 Projected Forced Outage Cost
Services
Spare Parts
OPEX
3,156,094.63
490,163.62
All figures are based on the actual Unit 1 June 2022 UMO OPEX from Finance
Consumables
-
PHP
3,646,258.25
PHP/unit
7.38
86.25
58.20
PHP
2,634,807.60
228,038.96
7,261,713.52
2.3 Projected Start-up Cost after Forced Outage
Feedback Power, MWh
Demineralized Water, m3
Diesel Oil, liters
Consumption
357.02
2,643.93
124,771.71
Document Code:
PPR-TSD-23-004
Effective Date:
February 9, 2023
Plant Performance Report: Semirara Coal: Effect on Boiler Operation and Economical Price Determination
Silica Sand, MT
Limestone, MT
56.19
34.23
Revision:
0
Page:
17 of 17
7,062.14
1,964.29
396,808.13
67,245.35
10,588,613.56
Feedback power based on the actual consumption last September 28-29, 2022 during Unit 3 tripping and last October 2628, 2022 during start-up
Demineralized water based on the actual consumption last October 20-28, 2022 during Unit 3 start-up
Diesel oil and silica sand based on the actual consumption last October 27-28, 2022 during Unit 3 start-up
Limestone based on the actual consumption last October 28, 2022 during Unit 3 start-up
Appendix C Year 2 of 2 Indo 1 Semirara coal firing
1. Total Projected Operational Cost, PHP
1.1 Projected Cost of Coal Consumed
MT/day
Indonesian Coal
1,287.42
Semirara Coal
638.96
5,080,078,134.90
Days
344
344
PHP/MT
7,933.92
6,968.47
PHP
3,513,729,267.11
1,531,688,024.02
5,045,417,291.13
MT/day based on the average daily feeder-based coal consumption of Unit 3 when in 2 Indo 1 Semirara coal firing and at
least 95% net capacity factor
1.2 Projected Cost of Silica Sand Consumed
MT/day
Days
PHP/MT
PHP
Silica Sand
3.15
344
7,062.14
7,654,786.54
MT/day based on the average daily formula-based silica sand consumption of Unit 3 when in 2 Indo 1 Semirara coal firing
1.3 Projected Cost of Limestone Consumed
MT/day
Days
PHP/MT
PHP
Limestone
31.57
344
1,964.29
21,333,969.17
MT/day based on the average daily formula-based limestone consumption of Unit 3 when in 2 Indo 1 Semirara coal firing
1.4 Projected Cost of Demineralized Water Consumed
m3/day
Days
Demineralized Water
191.17
344
3
m /day based on the average daily demineralized water consumption of Unit 3
PHP/m3
86.25
PHP
5,672,088.08