CN101451070B - Coke making and coal blending method based on catalytic index - Google Patents

Abstract

The invention relates to a coking and coal blending method based on catalytic index. The method comprises the following specific steps: 1, respectively detecting components of various single coal ashes participating in coal blending to at least obtain the mass contents of Fe2O3, K2O, Na2O, CaO, BaO, MgO, MnO, SiO2, Al2O3 and TiO2 of each single coal; 2, respectively detecting a dry-based ash component and a dry-based volatile component of various single coals participating in coal blending; 3, selecting the single coal participating in coal blending; 4, designing the mass contents of the various single coals participating in coal blending in blended coal; 5, calculation, which specifically comprises: a catalyst index of the coal ash component of the blended coal is calculated; and 6, judgment, which specifically comprises: MCIb4 less than or equal to 4 is judged to be qualified; and otherwise, the MCIb<=4 is unqualified. The coking and coal blending method increases the catalytic index and can further improve stability of the quality of the blended coal, thereby further improving the quality of coke.

Description

Coke making and coal blending method based on catalytic index

Technical field

The present invention relates to coke making and coal blending technical field, particularly coke making and coal blending method.

Background technology

Coke is one of main raw material of blast furnace ironmaking production, and the quality of coke quality directly influences the process and the metallurgical effect of blast-furnace smelting.So producing the coke that can satisfy the blast furnace requirement is the assurance of smooth operation of furnace, producing high grade coke is that blast furnace guarantees efficiently.

Scientific research and production practice show that all coke quality depends primarily on the quality of mixed coal and is equipped with coal, coking manufacturing condition.Under the certain situation of processing condition, coke quality depends primarily on the quality of mixed coal.And mixed coal is to be cooperated by multiple coal such as bottle coal, gas-fat coal, 1/3 coking coal, rich coal, coking coal, lean coal to form.The selection of the further investigation of therefore, the selection of each single kind coal, single kind coal character, the selection of blending ratio, mixed coal mass parameter and definite most important.

In traditional coke making and coal blending method, generally only consider A _d, V _Daf, S _{T, d}, G, Y coal blending index, only use these coal blending indexs as the coal blending parameter, the mixed coal quality fluctuation of allotting is bigger, thereby has influenced the quality of coke.

In addition, people remove and consider conventional coal index (A when the ature of coal characteristic of the single kind of research coal _d, V _Daf, S _{T, d}, G, Y) outside, also comprise through single components of coal ash of planting coal and calculate single catalytic index of planting the components of coal ash of coal.

For example certain single components of coal ash of planting is seen table 1:

Certain single components of coal ash of planting of table 1

Its catalytic index is:

$\mathrm{MCI}=A_d\frac{{\mathrm{Fe}}_2{O}_3+1.85K_{2}O+2.2{\mathrm{Na}}_{2}O+1.6\mathrm{CaO}+1.91\mathrm{BaO}+0.83\mathrm{MgO}+0.9\mathrm{MnO}}{(100-V_d)(\mathrm{Si}{O}_2+0.41{\mathrm{Al}}_2{O}_3+2.5\mathrm{Ti}{O}_2)}\&times;100$

$=14.17$

In the formula:

MCI---single ash component catalytic index of planting coal;

A _d---single dry basis ash content of planting coal, unit: %;

Fe ₂O ₃---Fe in the ash component of single kind coal ₂O ₃Mass content, unit: %;

K ₂O---K in the ash component of single kind coal ₂The mass content of O, unit: %;

Na ₂O---Na in the ash component of single kind coal ₂The mass content of O, unit: %;

CaO---the mass content of CaO in the ash component of single kind coal, unit: %;

BaO---the mass content of BaO in the ash component of single kind coal, unit: %;

MgO---the mass content of MgO in the ash component of single kind coal, unit: %;

MnO---the mass content of MnO in the ash component of single kind coal, unit: %;

SiO ₂---SiO in the ash component of single kind coal ₂Mass content, unit: %;

Al ₂O ₃---Al in the ash component of single kind coal ₂O ₃Mass content, unit: %;

TiO ₂---TiO in the ash component of single kind coal ₂Mass content, unit: %;

V _d---single butt volatile matter of planting coal, unit: %.

At present, catalytic index only is used for single ature of coal The Characteristics of planting coal, is not used in the production practice of coke making and coal blending method.

Summary of the invention

Technical problem to be solved by this invention is: a kind of coke making and coal blending method based on catalytic index is provided; This coke making and coal blending method selects suitable mixed coal mass parameter to participate in coal blending; Further improve the mixed coal quality of stability, thereby further improved the quality of coke.

The present invention solves the problems of the technologies described above the technical scheme that is adopted:

Based on the coke making and coal blending method of catalytic index, its concrete steps are:

(1) detects the single step of planting components of coal ash that to participate in coal blending respectively;

This step obtains each single Fe that plants coal at least ₂O ₃, K ₂O, Na ₂O, CaO, BaO, MgO, MnO, SiO ₂, Al ₂O ₃, TiO ₂Mass content;

(2) detection can be participated in each the single dry basis ash content of coal and step of butt volatile matter of planting of coal blending respectively;

(3) selected single step of planting coal of participating in coal blending;

(4) each single step of planting coal mass content in mixed coal of coal blending is participated in design;

(5) step of calculating is specially:

Calculate the catalytic index of the components of coal ash of mixed coal:

$\mathrm{MC}{I}_b={\left(A_d\right)}_b\frac{{\left({\mathrm{Fe}}_2{O}_3\right)}_b+1.85{\left(K_{2}O\right)}_b+2.2{\left({\mathrm{Na}}_{2}O\right)}_b+1.6{\left(\mathrm{CaO}\right)}_b+1.91{\left(\mathrm{BaO}\right)}_b+0.83{\left(\mathrm{MgO}\right)}_b+0.9{\left(\mathrm{MnO}\right)}_b}{[100-{\left(V_d\right)}_b][{\left(\mathrm{Si}{O}_2\right)}_b+0.41{\left({\mathrm{Al}}_2{O}_3\right)}_b+2.5{\left(\mathrm{Ti}{O}_2\right)}_b}\&times;100$

In the formula:

MCI _b---the ash component catalytic index of mixed coal;

(A _d) _b---the dry basis ash content of mixed coal, unit: %;

(A _d) _b＝∑X _iA _di

(Fe ₂O ₃) _b---Fe in the ash component of mixed coal ₂O ₃Mass content, unit: %;

(Fe ₂O ₃) _b＝∑X _i(Fe ₂O ₃) _i

(K ₂O) _b---K in the ash component of mixed coal ₂The mass content of O, unit: %;

(K ₂O) _b＝∑X _i(K ₂O) _i

(Na ₂O) _b---Na in the ash component of mixed coal ₂The mass content of O, unit: %;

(Na ₂O) _b＝∑X _i(Na ₂O) _i

(CaO) _b---the mass content of CaO in the ash component of mixed coal, unit: %;

(CaO) _b＝∑X _i(CaO) _i

(BaO) _b---the mass content of BaO in the ash component of mixed coal, unit: %;

(BaO) _b＝∑X _i(BaO) _i

(MgO) _b---the mass content of MgO in the ash component of mixed coal, unit: %;

(MgO) _b＝∑X _i(MgO) _i

(MnO) _b---the mass content of MnO in the ash component of mixed coal, unit: %;

(MnO) _b＝∑X _i(MnO) _i

(SiO ₂) _b---SiO in the ash component of mixed coal ₂Mass content, unit: %;

(SiO ₂) _b＝∑X _i(SiO ₂) _i

(Al ₂O ₃) _b---Al in the ash component of mixed coal ₂O ₃Mass content, unit: %;

(Al ₂O ₃) _b＝∑X _i(Al ₂O ₃) _i

(TiO ₂) _b---TiO in the ash component of mixed coal ₂Mass content, unit: %;

(TiO ₂) _b＝∑X _i(TiO ₂) _i

(V _d) _b---the butt volatile matter of mixed coal, unit: %;

(V _d) _b＝∑X _iV _di

Wherein:

X _i---the single mass content of coal i in mixed coal, unit: % of planting;

A _Di---single dry basis ash content of planting coal i, unit: %;

(Fe ₂O ₃) _i---Fe in the ash component of single kind coal i ₂O ₃Mass content, unit: %;

(K ₂O) _i---K in the ash component of single kind coal i ₂The mass content of O, unit: %;

(Na ₂O) _i---Na in the ash component of single kind coal i ₂The mass content of O, unit: %;

(CaO) _i---the mass content of CaO in the ash component of single kind coal i, unit: %;

(BaO) _i---the mass content of BaO in the ash component of single kind coal i, unit: %;

(MgO) _i---the mass content of MgO in the ash component of single kind coal i, unit: %;

(MnO) _i---the mass content of MnO in the ash component of single kind coal i, unit: %;

(SiO ₂) _i---SiO in the ash component of single kind coal i ₂Mass content, unit: %;

(Al ₂O ₃) _i---Al in the ash component of single kind coal i ₂O ₃Mass content, unit: %;

(TiO ₂) _i---TiO in the ash component of single kind coal i ₂Mass content, unit: %;

V _Di---single butt volatile matter of planting coal i, unit: %.

(6) step of judging is specially: MCI _b≤4 is qualified, otherwise defective.

Above-mentioned coke making and coal blending method also comprises:

(7) result who obtains according to step (6) makes the following choice:

Qualified, finish;

Or,

Defective, selected again single coal, repeating step (3) of planting of participating in coal blending;

Or,

Defective, each single coal mass content in mixed coal, repeating step (4) of planting of coal blending is participated in design again.

The principle of coke making and coal blending method of the present invention:

Ash component is that coke carbon dissolves the damage catalyst for reaction, and different ash components have different catalytic performances.Result of study shows: K ₂O, Na ₂O, MgO, CaO, BaO, V ₂O ₅, MnO ₂, Fe ₂O ₃, CuO, PbO ₂, ZnO is the positive catalyst that carbon dissolve to decrease reaction; B ₂O ₃, TiO ₂Be that carbon dissolves the negative contact agent that decreases reaction, i.e. passivator; Al ₂O ₃, SiO ₂Carbon is dissolved the damage reaction to work hardly.

Catalytic index is represented the comprehensive katalysis of ash component, dissolves damage level of response (being the hot performance of coke) with the reactive CRI of coke and the carbon of post-reaction strength CSR sign coke.The hot performance of catalytic index STRENGTH ON COKE (reactive CRI and post-reaction strength CSR) influence significantly.Catalytic index and CRI positive correlation are with the CSR negative correlation.Therefore control the hot performance that the catalytic index of components of coal ash can the remarkably influenced coke.

The mineral composition of different coals also has nothing in common with each other, and the ash component variation range is very wide, directly influences the quality of coke, and and then influences blast-furnace smelting.To increase the alkali load of blast furnace like the alkali metal content height in the coal, the aggravation coke is in the granularity degraded at blast furnace stack position; The high quantity of slag and the mobile variation that makes slag that can increase blast furnace of oxygen content of coal aluminium content has problems when slag is used in Cement industry, also can have influence on the direct motion of blast furnace; Blast-melted sulphur content height also has direct relation with the sulphur in the coal; Phosphate minerals such as the phosphatic rock in the coal can be influential to blast-melted phosphorus content etc.

Coke making and coal blending method of the present invention increases the catalytic index index in coke making and coal blending method, can further improve the mixed coal quality of stability, thereby further improves the quality of coke.

Embodiment

The present invention is based on the coke making and coal blending method embodiment of catalytic index, its concrete steps are:

(1) detects the single step of planting components of coal ash that to participate in coal blending respectively;

This step obtains each single Fe that plants coal at least ₂O ₃, K ₂O, Na ₂O, CaO, BaO, MgO, MnO, SiO ₂, Al ₂O ₃, TiO ₂Mass content (detection method: GB/T1574 coal ash analysis method); See table 2:

(2) detection can be participated in each the single dry basis ash content of coal and step (detection method: the technical analysis method of GB/T212 coal) of butt volatile matter of planting of coal blending respectively;

(3) selected single step of planting coal of participating in coal blending; See table 3;

(4) each single step of planting coal mass content in mixed coal of coal blending is participated in design; See table 3;

Table 2 is for participating in single components of coal ash (unit: %) of planting of coal blending

Sequence number	A d	V d	SiO 2	Al 2O 3	Fe 2O 3	CaO	MgO	K 2O	Na 2O	TiO 2	MnO	BaO	MCI
														1	8.66	31.75	31.16	18.39	10.36	19.65	0.91	0.44	0.41	0.57	0.12	0.23	14.17
2	7.73	32.32	45.06	34.75	5.37	5.45	1.36	0.26	1.56	1.54	0.01	0.3	3.57
														3	9.8	30.62	46.21	37.57	4.37	5.06	0.82	0.59	0.39	1.87	0.07	0.039	3.25
4	7.44	33.62	44.76	36.5	7.94	4.33	0.96	0.24	0.65	1.62	0.26	0.24	3.20
														5	9.76	31.98	43.72	33.61	4.2	7.65	1.14	0.45	0.33	1.52	0.046	0.04	4.46
6	9.42	23.5	50.7	35.88	3.58	4.01	0.91	0.55	0.3	1.96	0.07	0.032	2.20
														7	9.73	26.01	46.94	33.7	9.07	4.98	0.62	0.54	0.31	1.36	0.13	0.032	3.98
8	9.69	22.02	51.63	36.82	4.57	3.3	0.28	0.53	0.35	1.6	0.028	0.053	2.10
														9	9.56	25.5	49.5	41.65	5.16	0.94	0.31	0.51	0.46	1.4	0.016	0.05	1.65
10	9.56	23.2	51.15	37.57	2.39	5.06	0.53	0.38	0.21	1.41	0.05	0.038	2.17
														11	9.46	26.84	53.73	24.48	5.94	7.57	1.5	0.47	0.33	1.42	0.05	0.13	4.07
12	9.77	23.75	46.79	31.18	12.75	4.13	0.6	0.59	0.58	1.18	0.09	0.027	4.58
														13	9.87	14.45	46.64	36.86	3.97	4.01	0.94	0.47	1.86	1.52	0.023	0.161	2.90
14	11.78	14.51	50.47	37.58	2.84	4.56	0.7	0.24	0.48	1.52	0.027	0.092	2.46

Single coal and each single coal mass content (unit: %) in mixed coal of planting that participates in coal blending of planting of the participation coal blending that table 3 is selected

(5) step of calculating is specially:

Calculate the catalytic index of the components of coal ash of mixed coal:

${\mathrm{MCI}}_b={\left(A_d\right)}_b\frac{{\left({\mathrm{Fe}}_2{O}_3\right)}_b+1.85{\left(K_{2}O\right)}_b+2.2{\left({\mathrm{Na}}_{2}O\right)}_b+1.6{\left(\mathrm{CaO}\right)}_b+1.91{\left(\mathrm{BaO}\right)}_b+0.83{\left(\mathrm{MgO}\right)}_b+0.9{\left(\mathrm{MnO}\right)}_b}{[100-{\left(V_d\right)}_b][{\left(\mathrm{Si}{O}_2\right)}_b+0.41{\left({\mathrm{Al}}_2{O}_3\right)}_b+2.5{\left({\mathrm{TiO}}_2\right)}_b]}\&times;100$

In the formula:

MCI _b---the ash component catalytic index of mixed coal;

(A _d) _b---the dry basis ash content of mixed coal, unit: %;

(A _d) _b=∑ X _iA _Di, be example with scheme 1:

(A _d) _b＝5*8.66+10*7.73+15*9.8+10*7.44+10*9.76+20*9.42+10*9.69+5*9.56+5*9.77+10*9.87

(Fe ₂O ₃) _b---Fe in the ash component of mixed coal ₂O ₃Mass content, unit: %;

(Fe ₂O ₃) _b＝∑X _i(Fe ₂O ₃) _i

(K ₂O) _b---K in the ash component of mixed coal ₂The mass content of O, unit: %;

(K ₂O) _b＝∑X _i(K ₂O) _i

(Na ₂O) _b---Na in the ash component of mixed coal ₂The mass content of O, unit: %;

(Na ₂O) _b＝∑X _i(Na ₂O) _i

(CaO) _b---the mass content of CaO in the ash component of mixed coal, unit: %;

(CaO) _b＝∑X _i(CaO) _i

(BaO) _b---the mass content of BaO in the ash component of mixed coal, unit: %;

(BaO) _b＝∑X _i(BaO) _i

(MgO) _b---the mass content of MgO in the ash component of mixed coal, unit: %;

(MgO) _b＝∑X _i(MgO) _i

(MnO) _b---the mass content of MnO in the ash component of mixed coal, unit: %;

(MnO) _b＝∑X _i(MnO) _i

(SiO ₂) _b---SiO in the ash component of mixed coal ₂Mass content, unit: %;

(SiO ₂) _b＝∑X _i(SiO ₂) _i

(Al ₂O ₃) _b---Al in the ash component of mixed coal ₂O ₃Mass content, unit: %;

(Al ₂O ₃) _b＝∑X _i(Al ₂O ₃) _i

(TiO ₂) _b---TiO in the ash component of mixed coal ₂Mass content, unit: %;

(TiO ₂) _b＝∑X _i(TiO ₂) _i

(V _d) _b---the butt volatile matter of mixed coal, unit: %;

(V _d) _b＝∑X _iV _di

Wherein:

X _i---the single mass content of coal i in mixed coal, unit: % of planting in mixed coal;

A _Di---single dry basis ash content of planting coal i, unit: %;

(Fe ₂O ₃) _i---Fe in the ash component of single kind coal i ₂O ₃Mass content, unit: %;

(K ₂O) _i---K in the ash component of single kind coal i ₂The mass content of O, unit: %;

(Na ₂O) _i---Na in the ash component of single kind coal i ₂The mass content of O, unit: %;

(CaO) _i---the mass content of CaO in the ash component of single kind coal i, unit: %;

(BaO) _i---the mass content of BaO in the ash component of single kind coal i, unit: %;

(MgO) _i---the mass content of MgO in the ash component of single kind coal i, unit: %;

(MnO) _i---the mass content of MnO in the ash component of single kind coal i, unit: %;

(SiO ₂) _i---SiO in the ash component of single kind coal i ₂Mass content, unit: %;

(Al ₂O ₃) _i---Al in the ash component of single kind coal i ₂O ₃Mass content, unit: %;

(TiO ₂) _i---TiO in the ash component of single kind coal i ₂Mass content, unit: %;

V _Di---single butt volatile matter of planting coal i, unit: %.

(6) step of judging is specially: MCI _b≤4 is qualified, otherwise defective.

The catalytic index MCI of scheme 1 _b=3.37.Produce the gained coke quality: shatter strength M40=87.2%, abrasive wear resistance M10=6.2%, reactive CRI=24.1%, post-reaction strength CSR=67.5%.

The catalytic index MCI of scheme 2 _b=3.44.Actual production gained coke quality: shatter strength M40=87.0%, abrasive wear resistance M10=6.3%, reactive CRI=24.5%, post-reaction strength CSR=67.1%.

The catalytic index MCI of scheme 3 _b=3.60.Actual production gained coke quality: shatter strength M40=86.8%, abrasive wear resistance M10=6.4%, reactive CRI=24.6%, post-reaction strength CSR=66.8%.

The catalytic index MCI of scheme 4 _b=3.82.Actual production gained coke quality: shatter strength M40=86.5%, abrasive wear resistance M10=6.5%, reactive CRI=24.9%, post-reaction strength CSR=66.1%.

The catalytic index MCI of scheme 5 _b=5.24.Actual production gained coke quality: shatter strength M40=83.5%, abrasive wear resistance M10=7.3%, reactive CRI=29.2%, post-reaction strength CSR=59.2%.

The MCI of scheme 1-4 _bAll qualified, actual production gained coke quality is also qualified.The MCI of scheme 5 _bDefective, the reactive CRI in the actual production gained coke quality, post-reaction strength CSR index is defective.

(7) result who obtains according to step (6) makes the following choice:

Qualified, finish;

Or,

Defective, selected again single coal, repeating step (3) of planting of participating in coal blending;

Or,

Defective, each single coal mass content in mixed coal, repeating step (4) of planting of coal blending is participated in design again.

Claims (2)

1. based on the coke making and coal blending method of catalytic index, its concrete steps are:

(1) detects the single step of planting components of coal ash that to participate in coal blending respectively;

This step obtains each single Fe that plants coal at least ₂O ₃, K ₂O, Na ₂O, CaO, BaO, MgO, MnO, SiO ₂, Al ₂O ₃, TiO ₂Mass content;

(2) detection can be participated in each the single dry basis ash content of coal and step of butt volatile matter of planting of coal blending respectively;

(3) selected single step of planting coal of participating in coal blending;

(4) each single step of planting coal mass content in mixed coal of coal blending is participated in design;

(5) step of calculating is specially:

Calculate the catalytic index of the components of coal ash of mixed coal:

${\mathrm{MCI}}_b={\left(A_d\right)}_b=\frac{{\left({\mathrm{Fe}}_2{O}_3\right)}_b+1.85{\left(K_{2}O\right)}_b+2.2{\left({\mathrm{Na}}_{2}O\right)}_b+1.6{\left(\mathrm{CaO}\right)}_b+1.91{\left(\mathrm{BaO}\right)}_b+0.83{\left(\mathrm{MgO}\right)}_b+0.9{\left(\mathrm{MnO}\right)}_b}{[100-{\left(V_d\right)}_b][{\left({\mathrm{SiO}}_2\right)}_b+0.41{\left({\mathrm{Al}}_2{O}_3\right)}_b+2.5{\left({\mathrm{TiO}}_2\right)}_b]}\&times;100$

In the formula:

MCI _b---the ash component catalytic index of mixed coal;

(A _d) _b---the dry basis ash content of mixed coal, unit: %;

(A _d) _b＝∑X _iA _di

(Fe ₂O ₃) _b---Fe in the ash component of mixed coal ₂O ₃Mass content, unit: %;

(Fe ₂O ₃) _b＝∑X _i(Fe ₂O ₃) _i

(K ₂O) _b---K in the ash component of mixed coal ₂The mass content of O, unit: %;

(K ₂O) _b＝∑X _i(K ₂O) _i

(Na ₂O) _b---Na in the ash component of mixed coal ₂The mass content of O, unit: %;

(Na ₂O) _b＝∑X _i(Na ₂O) _i

(CaO) _b---the mass content of CaO in the ash component of mixed coal, unit: %;

(CaO) _b＝∑X _i(CaO) _i

(BaO) _b---the mass content of BaO in the ash component of mixed coal, unit: %;

(BaO) _b＝∑X _i(BaO) _i

(MgO) _b---the mass content of MgO in the ash component of mixed coal, unit: %;

(MgO) _b＝∑X _i(MgO) _i

(MnO) _b---the mass content of MnO in the ash component of mixed coal, unit: %;

(MnO) _b＝∑X _i(MnO) _i

(SiO ₂) _b---SiO in the ash component of mixed coal ₂Mass content, unit: %;

(SiO ₂) _b＝∑X _i(SiO ₂) _i

(Al ₂O ₃) _b---Al in the ash component of mixed coal ₂O ₃Mass content, unit: %;

(Al ₂O ₃) _b＝∑X _i(Al ₂O ₃) _i

(TiO ₂) _b---TiO in the ash component of mixed coal ₂Mass content, unit: %;

(TiO ₂) _b＝∑X _i(TiO ₂) _i

(V _d) _b---the butt volatile matter of mixed coal, unit: %;

(V _d) _b＝∑X _iVd _i

Wherein:

X _i---the single mass content of coal i in mixed coal, unit: % of planting in mixed coal;

A _Di---single dry basis ash content of planting coal i, unit: %;

(Fe ₂O ₃) _i---Fe in the ash component of single kind coal i ₂O ₃Mass content, unit: %;

(K ₂O) _i---K in the ash component of single kind coal i ₂The mass content of O, unit: %;

(Na ₂O) _i---Na in the ash component of single kind coal i ₂The mass content of O, unit: %;

(CaO) _i---the mass content of CaO in the ash component of single kind coal i, unit: %;

(BaO) _i---the mass content of BaO in the ash component of single kind coal i, unit: %;

(MgO) _i---the mass content of MgO in the ash component of single kind coal i, unit: %;

(MnO) _i---the mass content of MnO in the ash component of single kind coal i, unit: %;

(SiO ₂) _i---SiO in the ash component of single kind coal i ₂Mass content, unit: %;

(Al ₂O ₃) _i---Al in the ash component of single kind coal i ₂O ₃Mass content, unit: %;

(TiO ₂) _i---TiO in the ash component of single kind coal i ₂Mass content, unit: %;

V _Di---single butt volatile matter of planting coal i, unit: %.

(6) step of judging is specially: MCI _b≤4 is qualified, otherwise defective.

2. coke making and coal blending method as claimed in claim 1, it is characterized in that: it also comprises:

(7) result who obtains according to step (6) makes the following choice:

Qualified, finish;

Or,

Defective, repeating step (3);

Or,

Defective, repeating step (4).